Magnetic tape having characterized magnetic layer surface, magnetic tape cartridge, and magnetic tape device

ABSTRACT

A magnetic tape in which a tape thickness of the magnetic tape is 5.2 μm or less, and in an environment with a temperature of 23° C. and a relative humidity of 50%, an AlFeSil abrasion value45° of a surface of the magnetic layer measured at a tilt angle of 45° of an AlFeSil prism is 20 μm to 50 μm, a standard deviation of an AlFeSil abrasion value of the surface of the magnetic layer measured at each of tilt angles of 0°, 15°, 30°, and 45° of the AlFeSil prism is 30 μm or less, and the tilt angle of the AlFeSil prism is an angle formed by a longitudinal direction of the AlFeSil prism and a width direction of the magnetic tape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2021-158788 filed on Sep. 29, 2021 and Japanese PatentApplication No. 2022-145715 filed on Sep. 14, 2022. Each of the aboveapplications is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tapecartridge, and a magnetic tape device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up or archives (for example, seeJP2016-524774A and US2019/0164573A1).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed bycausing the magnetic tape to run in a magnetic tape device and causing amagnetic head to follow a data band of the magnetic tape to record dataon the data band. Accordingly, a data track is formed on the data band.In addition, in a case of reproducing the recorded data, the magnetictape is caused to run in the magnetic tape device and the magnetic headis caused to follow the data band of the magnetic tape, thereby readingdata recorded on the data band.

In order to increase an accuracy with which the magnetic head followsthe data band of the magnetic tape in the recording and/or thereproducing, a system that performs head tracking using a servo signal(hereinafter, referred to as a “servo system”) is practiced.

In addition, it is proposed that dimensional information of a magnetictape during running in a width direction (contraction, expansion, or thelike) is obtained using the servo signal and an angle for tilting anaxial direction of a module of a magnetic head with respect to the widthdirection of the magnetic tape (hereinafter, also referred to as a “headtilt angle”) is changed according to the obtained dimensionalinformation (see JP6590102B and US2019/0164573A1, for example,paragraphs 0059 to 0067 and paragraph 0084 of JP6590102B). During therecording or the reproducing, in a case where the magnetic head forrecording or reproducing data records or reproduces data while beingdeviated from a target track position due to width deformation of themagnetic tape, phenomenons such as overwriting on recorded data,reproducing failure, and the like may occur. The present inventorsconsider that changing the angle as described above is one of a unit forsuppressing the occurrence of such a phenomenon. For example, assumingthat the head tilt angle is changed as described above, a magnetic tapein which a deterioration in electromagnetic conversion characteristicsis small, in a case of recording and/or reproducing data at differenthead tilt angles is desirable.

One aspect of the present invention is to provide a magnetic tape havinga small deterioration in electromagnetic conversion characteristics in acase of recording and/or reproducing data at different head tilt angles.

An aspect of the invention is as follows.

(1) A magnetic tape comprising:

-   -   a non-magnetic support; and    -   a magnetic layer containing a ferromagnetic powder,    -   wherein a tape thickness of the magnetic tape is 5.2 μm or less,        and    -   in an environment with a temperature of 23° C. and a relative        humidity of 50%,    -   an AlFeSil abrasion value_(45°) of a surface of the magnetic        layer measured at a tilt angle of 45° of an AlFeSil prism is 20        μm to 50 μm,    -   a standard deviation of an AlFeSil abrasion value of the surface        of the magnetic layer measured at each of tilt angles of 0°,        15°, 30°, and 45° of the AlFeSil prism (hereinafter, also simply        referred to as a “standard deviation of AlFeSil abrasion value”)        is 30 μm or less, and the tilt angle of the AlFeSil prism is an        angle formed by a longitudinal direction of the AlFeSil prism        and a width direction of the magnetic tape.        (2) The magnetic tape according to (1),    -   wherein the standard deviation of the AlFeSil abrasion value is        15 μm to 30 μm.        (3) The magnetic tape according to (1) or (2),    -   wherein the tape thickness is 4.0 μm to 5.2 μm.        (4) The magnetic tape according to any one of (1) to (3),    -   wherein the tape thickness is 4.0 μm to 5.0 μm.        (5) The magnetic tape according to any one of (1) to (4),    -   wherein a standard deviation of curvature of the magnetic tape        in a longitudinal direction (hereinafter, also simply referred        to as a “standard deviation of curvature”) is 5 mm/m or less.        (6) The magnetic tape according to any one of (1) to (5),    -   wherein the magnetic layer contains one or more kinds of        non-magnetic powder.        (7) The magnetic tape according to (6),    -   wherein the non-magnetic powder includes an alumina powder.        (8) The magnetic tape according to any one of (1) to (7),        further comprising:    -   a non-magnetic layer containing a non-magnetic powder between        the non-magnetic support and the magnetic layer.        (9) The magnetic tape according to (8),    -   wherein a thickness of the non-magnetic layer is 0.1 μm to 0.7        μm.        (10) The magnetic tape according to any one of (1) to (9),        further comprising:    -   a back coating layer containing a non-magnetic powder on a        surface side of the non-magnetic support opposite to a surface        side provided with the magnetic layer.        (11) The magnetic tape device according to any one of (1) to        (10),    -   wherein a vertical squareness ratio of the magnetic tape is 0.60        or more.        (12) The magnetic tape device according to any one of (1) to        (11),    -   wherein a vertical squareness ratio of the magnetic tape is 0.65        or more.        (13) A magnetic tape cartridge comprising:    -   the magnetic tape according to any one of (1) to (12).        (14) A magnetic tape device comprising:    -   the magnetic tape according to any one of (1) to (12).        (15) The magnetic tape device according to (14), further        comprising:    -   a magnetic head,    -   wherein the magnetic head includes a module including an element        array having a plurality of magnetic head elements between a        pair of servo signal reading elements, and    -   the magnetic tape device changes an angle θ formed by an axis of        the element array with respect to the width direction of the        magnetic tape during running of the magnetic tape in the        magnetic tape device.

According to one aspect of the present invention, it is possible toprovide a magnetic tape having a small deterioration in electromagneticconversion characteristics in a case of recording and/or reproducingdata at different head tilt angles. In addition, according to one aspectof the invention, it is possible to provide a magnetic tape cartridgeand a magnetic tape device including the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a module of a magnetichead.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween a module and a magnetic tape during running of the magnetic tapein a magnetic tape device.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

FIG. 4 is an explanatory diagram of a curvature of a magnetic tape in alongitudinal direction.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear tape-open(LTO) Ultrium format tape.

FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape.

FIG. 8 is a schematic view showing an example of the magnetic tapedevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

An aspect of the invention relates to a magnetic tape including anon-magnetic support, and a magnetic layer containing a ferromagneticpowder. A tape thickness of the magnetic tape is 5.2 μm or less. Inaddition, in an environment with a temperature of 23° and a relativehumidity of 50%, an AlFeSil abrasion value_(45°) of a surface of themagnetic layer measured at a tilt angle of 45° of an AlFeSil prism ofthe magnetic tape is 20 μm to 50 μm, and a standard deviation of anAlFeSil abrasion value of the surface of the magnetic layer measured ateach of tilt angles of 0°, 15°, 30°, and 45° of the AlFeSil prism is 30μm or less. In the invention and the specification, the “surface of themagnetic layer” is identical to a surface of the magnetic tape on themagnetic layer side.

Description of Head Tilt Angle

Prior to the description of the tilt angle of the AlFeSil prism, aconfiguration of the magnetic head, a head tilt angle, and the like willbe described. In addition, a reason why it is considered that thephenomenon occurring during the recording or during the reproducingdescribed above can be suppressed by tilting an axial direction of themodule of the magnetic head with respect to the width direction of themagnetic tape while the magnetic tape is running will also be describedlater.

The magnetic head may include one or more modules including an elementarray including a plurality of magnetic head elements between a pair ofservo signal reading elements, and can include two or more modules orthree or more modules. The total number of such modules can be, forexample, 5 or less, 4 or less, or 3 or less, or the magnetic head mayinclude the number of modules exceeding the total number exemplifiedhere. Examples of arrangement of the plurality of modules can include“recording module-reproducing module” (total number of modules: 2),“recording module-reproducing module-recording module” (total number ofmodules: 3), and the like. However, the invention is not limited to theexamples shown here.

Each module can include an element array including a plurality ofmagnetic head elements between a pair of servo signal reading elements,that is, arrangement of elements. The module including a recordingelement as the magnetic head element is a recording module for recordingdata on the magnetic tape. The module including a reproducing element asthe magnetic head element is a reproducing module for reproducing datarecorded on the magnetic tape. In the magnetic head, the plurality ofmodules are arranged, for example, in a recording and reproducing headunit so that an axis of the element array of each module is oriented inparallel. The “parallel” does not mean only parallel in the strictsense, but also includes a range of errors normally allowed in thetechnical field of the invention. For example, the range of errors meansa range of less than ±10° from an exact parallel direction.

In each element array, the pair of servo signal reading elements and theplurality of magnetic head elements (that is, recording elements orreproducing elements) are usually arranged to be in a straight linespaced apart from each other. Here, the expression that “arranged in astraight line” means that each magnetic head element is arranged on astraight line connecting a central portion of one servo signal readingelement and a central portion of the other servo signal reading element.The “axis of the element array” in the present invention and the presentspecification means the straight line connecting the central portion ofone servo signal reading element and the central portion of the otherservo signal reading element.

Next, the configuration of the module and the like will be furtherdescribed with reference to the drawings. However, the aspect shown inthe drawings is an example and the invention is not limited thereto.

FIG. 1 is a schematic view showing an example of a module of a magnetichead. The module shown in FIG. 1 includes a plurality of magnetic headelements between a pair of servo signal reading elements (servo signalreading elements 1 and 2). The magnetic head element is also referred toas a “channel”. “Ch” in the drawing is an abbreviation for a channel.The module shown in FIG. 1 includes a total of 32 reproducing elementsof Ch0 to Ch31.

In FIG. 1 , “L” is a distance between the pair of servo signal readingelements, that is, a distance between one servo signal reading elementand the other servo signal reading element. In the module shown in FIG.1 , the “L” is a distance between the servo signal reading element 1 andthe servo signal reading element 2. Specifically, the “L” is a distancebetween a central portion of the servo signal reading element 1 and acentral portion of the servo signal reading element 2. Such a distancecan be measured by, for example, an optical microscope or the like.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween the module and the magnetic tape during running of the magnetictape in the magnetic tape device. In FIG. 2 , a dotted line A indicatesa width direction of the magnetic tape. A dotted line B indicates anaxis of the element array. An angle θ can be the head tilt angle duringthe running of the magnetic tape, and is an angle formed by the dottedline A and the dotted line B. During the running of the magnetic tape,in a case where the angle θ is 0°, a distance in a width direction ofthe magnetic tape between one servo signal reading element and the otherservo signal reading element of the element array (hereinafter, alsoreferred to as an “effective distance between servo signal readingelements”) is “L”. On the other hand, in a case where the angle θexceeds 0°, the effective distance between the servo signal readingelements is “L cos θ” and the L cos θ is smaller than the L. That is, “Lcos θ<L”.

As described above, during the recording or the reproducing, in a casewhere the magnetic head for recording or reproducing data records orreproduces data while being deviated from a target track position due towidth deformation of the magnetic tape, phenomenons such as overwritingon recorded data, reproducing failure, and the like may occur. Forexample, in a case where a width of the magnetic tape contracts orextends, a phenomenon may occur in which the magnetic head element thatshould record or reproduce at a target track position records orreproduces at a different track position. In addition, in a case wherethe width of the magnetic tape extends, the effective distance betweenthe servo signal reading elements may be shortened than a spacing of twoadjacent servo bands with a data band interposed therebetween (alsoreferred to as a “servo band spacing” or “spacing of servo bands”,specifically, a distance between the two servo bands in the widthdirection of the magnetic tape), and a phenomenon in that the data isnot recorded or reproduced at a part close to an edge of the magnetictape can occur.

With respect to this, in a case where the element array is tilted at theangle θ exceeding 0°, the effective distance between the servo signalreading elements becomes “L cos θ” as described above. The larger thevalue of θ, the smaller the value of L cos θ, and the smaller the valueof θ, the larger the value of L cos θ. Accordingly, in a case where thevalue of θ is changed according to a degree of dimensional change (thatis, contraction or expansion) in the width direction of the magnetictape, the effective distance between the servo signal reading elementscan be brought closer to or matched with the spacing of the servo bands.Therefore, during the recording or the reproducing, it is possible toprevent the occurrence of phenomenons such as overwriting on recordeddata, reproducing failure, and the like caused in a case where themagnetic head for recording or reproducing data records or reproducesdata while being deviated from a target track position due to widthdeformation of the magnetic tape, or it is possible to reduce afrequency of occurrence thereof.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

The angle θ at the start of running, θ_(initial), can be set to, forexample, 0° or more or more than 0°.

In FIG. 3 , a central diagram shows a state of the module at the startof running.

In FIG. 3 , a right diagram shows a state of the module in a case wherethe angle θ is set to an angle θ_(c) which is a larger angle than theθ_(initial). The effective distance between the servo signal readingelements L cos θ_(c) is a value smaller than L cos θ_(initial) at thestart of running of the magnetic tape. In a case where the width of themagnetic tape is contracted during the running of the magnetic tape, itis preferable to perform such angle adjustment.

On the other hand, in FIG. 3 , a left diagram shows a state of themodule in a case where the angle θ is set to an angle θ_(e) which is asmaller angle than the θ_(initial). The effective distance between theservo signal reading elements L cos θ_(e) is a value larger than L cosθ_(initial) at the start of running of the magnetic tape. In a casewhere the width of the magnetic tape is expanded during the running ofthe magnetic tape, it is preferable to perform such angle adjustment.

As described above, the change of the head tilt angle during the runningof the magnetic tape can contribute to prevention of the occurrence ofphenomenons such as overwriting on recorded data, reproducing failure,and the like caused in a case where the magnetic head for recording orreproducing data records or reproduces data while being deviated from atarget track position due to width deformation of the magnetic tape, orto reduction of a frequency of occurrence thereof.

Meanwhile, the recording of data on the magnetic tape and thereproducing of the recorded data are performed by bringing the surfaceof the magnetic layer of the magnetic tape into contact with themagnetic head and sliding. The inventors of the present inventionconsidered that, in a case where the head tilt angle changes during suchsliding, a contact state between the magnetic head and the surface ofthe magnetic layer can change and this can be a reason of adeterioration in electromagnetic conversion characteristics.Specifically, the inventors of the present invention considered that, ina case where the head tilt angle changes, a degree of abrasion of themagnetic head caused by the contact with the surface of the magneticlayer significantly changes, and accordingly, the electromagneticconversion characteristics deteriorates.

Based on the surmise described above, the present inventors conductedintensive studies. As a result, it is newly found that, regarding theabrasion property of the magnetic tape, by setting the AlFeSil abrasionvalue_(45°) measured at the tilt angle 45° of the AlFeSil prism and thestandard deviation of the AlFeSil abrasion value of the surface of themagnetic layer measured at each of tilt angles of 0°, 15°, 30°, and 45°of the AlFeSil prism, in the environment with the temperature of 23° anda relative humidity of 50%, to the ranges described above, thedeterioration in electromagnetic conversion characteristics can besuppressed in a case of performing recording and/or reproducing of dataat different head tilt angles. Hereinafter, the deterioration inelectromagnetic conversion characteristics in a case of performingrecording and/or reproducing of data at different head tilt angles isalso simply referred to as a “deterioration in electromagneticconversion characteristics”. The temperature and humidity of themeasurement environment are used as exemplary values of the temperatureand humidity of the use environment of the magnetic tape. Accordingly,the environment in which the data is recorded on the magnetic tape andthe recorded data is reproduced is not limited to the environment withthe temperature and the humidity described above. The tilt angle of theAlFeSil prism in a case of measuring the AlFeSil abrasion value is alsoused as an exemplary value of the angle that can be used in a case ofperforming the recording and/or reproducing of data by changing the headtilt angle during the running of the magnetic tape. Accordingly, thehead tilt angle in a case where the data is recorded on the magnetictape and the recorded data is reproduced is not limited to the angledescribed above. In addition, the present invention is not limited tothe inference of the inventors described in the present specification.

AlFeSil Abrasion Value_(45°) and Standard Deviation of AlFeSil AbrasionValue

Measuring Method

In the present invention and the present specification, the AlFeSilabrasion value at tilt angles of 0°, 15°, 30°, and 45° of the AlFeSilprism is a value measured by the following method in the environmentwith a temperature of 23° C. and a relative humidity of 50%.

An abrasion width of the AlFeSil prism, in a case where the magnetictape to be measured is caused to run under the following runningconditions using a reel tester, is measured. The AlFeSil prism is aprism made of AlFeSil, which is a sendust-based alloy. For theevaluation, the AlFeSil prism specified in European ComputerManufacturers Association (ECMA)-288/Annex H/H2 is used. For theabrasion width of the AlFeSil prism, an edge of the AlFeSil prism isobserved from the above using an optical microscope and an abrasionwidth described based on FIG. 1 of JP2007-026564A is obtained in aparagraph 0015 of JP2007-026564A.

The tilt angle of the AlFeSil prism (hereinafter, also simply referredto as a “tilt angle”) is an angle formed by the longitudinal directionof the AlFeSil prism and the width direction of the magnetic tape, andis defined in a range of 0° to 90°. In a case where the longitudinaldirection of the AlFeSil prism and the width direction of the magnetictape match, it is set to the tilt angle 0° of the AlFeSil prism, and ina case where the longitudinal direction of the AlFeSil prism and thelongitudinal direction of the magnetic tape, it is set to the tilt angle90° of the AlFeSil prism.

Running Conditions

At tilt angles of 0°, 15°, 30°, or 45° of the AlFeSil prism, the surfaceof the magnetic layer of the magnetic tape is brought into contact withone ridge side of the AlFeSil prism at a lap angle of 12°. In thisstate, a portion of the magnetic tape to be measured over a length of580 m in the longitudinal direction is caused to run at a speed of 3m/sec and reciprocated once.

In the measurement of the AlFeSil abrasion value at each tilt angle, atension applied in the longitudinal direction of the magnetic tapeduring the running is set to 1.0 N. Here, a value of the tension appliedin the longitudinal direction of the magnetic tape during the running isa set value of a reel tester. The AlFeSil abrasion width measured afterone round trip is defined as the AlFeSil abrasion value at each tiltangle. One unused AlFeSil prism that is not used in the measurement ofthe AlFeSil abrasion value is prepared. The measurement of the AlFeSilabrasion value at the above four different tilt angles is performed inan arbitrary order by bringing the surface of the magnetic layer intocontact with one ridge side of the four ridge sides of the AlFeSilabrasion value. The measurement of the AlFeSil abrasion value at eachtilt angle is performed on different portions of the magnetic tape to bemeasured. In addition, before the measurement at each tilt angle, themagnetic tape to be measured is left in a measurement environment for 24hours or longer in order to be familiar with the measurementenvironment.

Among the AlFeSil abrasion values obtained by the above method, theAlFeSil abrasion value obtained by the measurement at the tilt angle of45° is the AlFeSil abrasion value₄₅°. The standard deviation of theAlFeSil abrasion value obtained at the four different tilt angles (thatis, a positive square root of the dispersion) is set to the standarddeviation of the AlFeSil abrasion value of the magnetic tape to bemeasured.

AlFeSil Abrasion Value_(45°)

Regarding the abrasion property of the magnetic tape, the AlFeSilabrasion value_(45°) is 20 μm to 50 μm, from a viewpoint of suppressinga deterioration in electromagnetic conversion characteristics in a caseof performing the recording and/or reproducing of data at different headtilt angles. From a viewpoint of further suppressing the deteriorationin the electromagnetic conversion characteristics, the AlFeSil abrasionvalue_(45°) is preferably 45 μm or less, more preferably 40 μm or less,and even more preferably 35 μm or less. From the same viewpoint, theAlFeSil abrasion value_(45°) is preferably 23 μm or more, and morepreferably 25 μm or more.

Standard Deviation of AlFeSil Abrasion Value

The standard deviation of the AlFeSil abrasion value of the magnetictape is 30 μm or less, preferably 28 μm or less, more preferably 25 μmor less, even more preferably 23 μm or less, and still preferably 20 μmor less, from a viewpoint of suppressing a deterioration inelectromagnetic conversion characteristics in a case of performing therecording and/or reproducing of data at different head tilt angles. Thestandard deviation of the AlFeSil abrasion value can be, for example, 0μm or more, more than 0 μm, 1 μm or more, 3 μm or more, 5 μm or more, 7μm or more, 10 μm or more, 12 μm or more, or 15 μm or more. It ispreferable that the value of the standard deviation of the AlFeSilabrasion value is small, from a viewpoint of further suppressing thedeterioration in electromagnetic conversion characteristics.

The abrasion property of the magnetic tape can be adjusted, for example,according to a kind of component used for manufacturing the magneticlayer. The details of this point will be described later.

Tape Thickness

Regarding a tape thickness (total thickness) of the magnetic tape, ithas been required to increase recording capacity, that is, increase incapacity of the magnetic tape along with the enormous increase in amountof information in recent years. From a viewpoint of achieving highcapacity, the tape thickness of the magnetic tape is 5.2 μm or less. Byreducing the tape thickness of the magnetic tape, for example, a lengthof the magnetic tape accommodated in one reel of the magnetic tapecartridge can be increased, and accordingly, the high capacity can beachieved. From a viewpoint of further increasing high capacity, the tapethickness of the magnetic tape is preferably 5.0 μm or less and morepreferably 4.8 μm or less. In addition, from a viewpoint of ease ofhandling, the tape thickness of the magnetic tape is preferably 3.0 μmor more, more preferably 3.5 μm or more, and even more preferably 4.0 μmor more.

In the present invention and the present specification, the tapethickness of the magnetic tape is measured by the following method.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from arandom portion of the magnetic tape, these tape samples are overlapped,and the thickness is measured. A value which is one tenth of themeasured thickness (thickness per one tape sample) is set as the tapethickness. The thickness measurement can be performed using a well-knownmeasurement device capable of performing the thickness measurement at0.1 μm order.

Standard Deviation of Curvature

Next, a standard deviation of a curvature will be described.

The curvature of the magnetic tape in the longitudinal direction of thepresent invention and the present specification is a value obtained bythe following method in an environment of an atmosphere temperature of23° C. and a relative humidity of 50%. The magnetic tape is normallyaccommodated and circulated in a magnetic tape cartridge. As themagnetic tape to be measured, a magnetic tape taken out from an unusedmagnetic tape cartridge that is not attached to the magnetic tape deviceis used.

FIG. 4 is an explanatory diagram of the curvature of the magnetic tapein the longitudinal direction.

A tape sample having a length of 100 m in the longitudinal direction iscut out from a randomly selected portion of the magnetic tape to bemeasured. One end of this tape sample is defined as a position of 0 m,and a position spaced apart from this one end toward the other end by Dm (D meters) in the longitudinal direction is defined as a position of Dm. Accordingly, a position spaced apart by 10 m in the longitudinaldirection is defined as a position of 10 m, a position spaced apart by20 m is defined as a position of 20 m, and in this manner, a position of30 m, a position of 40 m, a position of 50 m, a position of 60 m, aposition of 70 m, a position of 80 m, a position of 90m, and a positionof 100 m are defined at intervals of 10 m sequentially.

A tape sample having a length of 1 m from the 0 m position to theposition of 1 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 0 m.

A tape sample having a length of 1 m from the 10 m position to theposition of 11 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 10 m.

A tape sample having a length of 1 m from the 20 m position to theposition of 21 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 20 m.

A tape sample having a length of 1 m from the 30 m position to theposition of 31 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 30 m.

A tape sample having a length of 1 m from the 40 m position to theposition of 41 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 40 m.

A tape sample having a length of 1 m from the 50 m position to theposition of 51 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 50 m.

A tape sample having a length of 1 m from the 60 m position to theposition of 61 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 60 m.

A tape sample having a length of 1 m from the 70 m position to theposition of 71 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 70 m.

A tape sample having a length of 1 m from the 80 m position to theposition of 81 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 80 m.

A tape sample having a length of 1 m from the 90 m position to theposition of 91 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 90 m.

A tape sample having a length of 1 m from the 99 m position to theposition of 100 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 100 m.

The tape sample of each position is hung for 24 hours±4 hours in atension-free state by gripping an upper end portion with a grippingmember (clip or the like) by setting the longitudinal direction as thevertical direction. Then, within 1 hour, the following measurement isperformed.

As shown in FIG. 4 , the tape piece is placed on a flat surface in atension-free state. The tape piece may be placed on a flat surface withthe surface on the magnetic layer side facing upward, or may be placedon a flat surface with the other surface facing upward. In FIG. 4 , Sindicates a tape sample and W indicates the width direction of the tapesample. Using an optical microscope, a distance L1 (unit: mm) that is ashortest distance between a virtual line 54 connecting both terminalportions 52 and 53 of the tape sample S and a maximum curved portion 55in the longitudinal direction of the tape sample S is measured. FIG. 4shows an example in which the tape sample is curved upward on a papersurface. Even in a case where the tape sample is curved downward, thedistance L1 (mm) is measured in the same manner. The distance L1 isdisplayed as a positive value regardless of which side is curved. In acase where no curve in the longitudinal direction is confirmed, the L1is set to 0 (zero) mm

By doing so, a standard deviation of the curvature L1 measured for atotal of 11 positions from the position of 0 m to the position of 100 m(that is, a positive square root of the dispersion) is the standarddeviation of the curvature of the magnetic tape to be measured in thelongitudinal direction (unit: mm/m).

In the magnetic tape, the standard deviation of the curvature obtainedby the method described above can be, for example, 7 mm/m or less and 6mm/m or less, and from a viewpoint of further suppressing adeterioration in electromagnetic conversion characteristics, it ispreferably 5 mm/m or less, more preferably 4 mm/m or less, and even morepreferably 3 mm/m or less. The standard deviation of the curvature ofthe magnetic tape can be, for example, 0 mm/m or more, more than 0 mm/m,1 mm/m or more, or 2 mm/m or more. It is preferable that the value ofthe standard deviation of the curvature is small, from a viewpoint offurther suppressing the deterioration in electromagnetic conversioncharacteristics.

The standard deviation of the curvature can be controlled by adjustingthe manufacturing conditions of the manufacturing step of the magnetictape. This point will be described later in detail.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder contained in the magnetic layer, awell-known ferromagnetic powder can be used as one kind or incombination of two or more kinds as the ferromagnetic powder used in themagnetic layer of various magnetic recording media. It is preferable touse a ferromagnetic powder having an average particle size as theferromagnetic powder, from a viewpoint of improvement of a recordingdensity. From this viewpoint, an average particle size of theferromagnetic powder is preferably equal to or smaller than 50 nm, morepreferably equal to or smaller than 45 nm, even more preferably equal toor smaller than 40 nm, further preferably equal to or smaller than 35nm, further more preferably equal to or smaller than 30 nm, further evenmore preferably equal to or smaller than 25 nm, and still preferablyequal to or smaller than 20 nm. Meanwhile, from a viewpoint of stabilityof magnetization, the average particle size of the ferromagnetic powderis preferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspectof the hexagonal ferrite powder will be described more specifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1,600 nm³. The atomized hexagonalstrontium ferrite powder showing the activation volume in the rangedescribed above is suitable for manufacturing a magnetic tape exhibitingexcellent electromagnetic conversion characteristics. The activationvolume of the hexagonal strontium ferrite powder is preferably equal toor greater than 800 nm³, and can also be, for example, equal to orgreater than 850 nm³. In addition, from a viewpoint of further improvingthe electromagnetic conversion characteristics, the activation volume ofthe hexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.Hc=2Ku/Ms{1−RkT/KuV)ln(At/0.693)^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom) satisfy a ratio of rareearth atom surface layer portion content/rare earth atom bulk content>1.0.

The content of rare earth atom of the hexagonal strontium ferrite powderwhich will be described later is identical to the rare earth atom bulkcontent. With respect to this, the partial dissolving using acid is todissolve the surface layer portion of particles configuring thehexagonal strontium ferrite powder, and accordingly, the content of rareearth atom in the solution obtained by the partial dissolving is thecontent of rare earth atom in the surface layer portion of the particlesconfiguring the hexagonal strontium ferrite powder. The rare earth atomsurface layer portion content satisfying a ratio of “rare earth atomsurface layer portion content/rare earth atom bulk content >1.0” meansthat the rare earth atoms are unevenly distributed in the surface layerportion (that is, a larger amount of the rare earth atoms is present,compared to that inside), among the particles configuring the hexagonalstrontium ferrite powder. The surface layer portion of the invention andthe specification means a part of the region of the particlesconfiguring the hexagonal strontium ferrite powder towards the insidefrom the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably in a range of 0.5 to 5.0 atom % with respect to 100 atom % ofthe iron atom. It is thought that the rare earth atom having the bulkcontent in the range described above and uneven distribution of the rareearth atom in the surface layer portion of the particles configuring thehexagonal strontium ferrite powder contribute to the prevention of adecrease in reproducing output during the repeated reproducing. It issurmised that this is because the rare earth atom having the bulkcontent in the range described above included in the hexagonal strontiumferrite powder and the uneven distribution of the rare earth atom in thesurface layer portion of the particles configuring the hexagonalstrontium ferrite powder can increase the anisotropy constant Ku. As thevalue of the anisotropy constant Ku is high, occurrence of a phenomenoncalled thermal fluctuation (that is, improvement of thermal stability)can be prevented. By preventing the occurrence of the thermalfluctuation, a decrease in reproducing output during the repeatedreproducing can be prevented. It is surmised that the unevendistribution of the rare earth atom in the surface layer portion of theparticles of the hexagonal strontium ferrite powder contributes tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvinghardness of the magnetic layer.

From a viewpoint of preventing reduction of the reproduction output inthe repeated reproduction and/or a viewpoint of further improvingrunning durability, the content of rare earth atom (bulk content) ismore preferably in a range of 0.5 to 4.5 atom %, even more preferably ina range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atoms are included, thebulk content is obtained from the total of the two or more kinds of rareearth atoms. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of preventing reduction of the reproduction outputduring the repeated reproduction include a neodymium atom, a samariumatom, an yttrium atom, and a dysprosium atom, a neodymium atom, asamarium atom, an yttrium atom are more preferable, and a neodymium atomis even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by,for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the filtrate obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, σs tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in σs. In one aspect, σs of thehexagonal strontium ferrite powder can be equal to or greater than 45A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On theother hand, from a viewpoint of noise reduction, σs is preferably equalto or smaller than 80 A×m²/kg and more preferably equal to or smallerthan 60 A×m²/kg. σs can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization σs is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, in a range of 2.0 to 15.0 atom % with respect to 100atom % of the iron atom. In one aspect, in the hexagonal strontiumferrite powder, the divalent metal atom included in this powder can beonly a strontium atom. In another aspect, the hexagonal strontiumferrite powder can also include one or more kinds of other divalentmetal atoms, in addition to the strontium atom. For example, thehexagonal strontium ferrite powder can include a barium atom and/or acalcium atom. In a case where the other divalent metal atom other thanthe strontium atom is included, a content of a barium atom and a contentof a calcium atom in the hexagonal strontium ferrite powder respectivelycan be, for example, in a range of 0.05 to 5.0 atom % with respect to100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one aspect, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint ofpreventing the reduction of the reproduction output during the repeatedreproduction, the hexagonal strontium ferrite powder includes the ironatom, the strontium atom, the oxygen atom, and the rare earth atom, anda content of the atoms other than these atoms is preferably equal to orsmaller than 10.0 atom %, more preferably in a range of 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one aspect, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting a value of the content (unit: % by mass)of each atom obtained by totally dissolving the hexagonal strontiumferrite powder into a value shown as atom % by using the atomic weightof each atom. In addition, in the invention and the specification, agiven atom which is “not included” means that the content thereofobtained by performing total dissolving and measurement by using an ICPanalysis device is 0% by mass. A detection limit of the ICP analysisdevice is generally equal to or smaller than 0.01 ppm (parts permillion) based on mass. The expression “not included” is used as ameaning including that a given atom is included with the amount smallerthan the detection limit of the ICP analysis device. In one aspect, thehexagonal strontium ferrite powder does not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp. 5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably in a rangeof 300 to 1,500 nm³. The atomized ε-iron oxide powder showing theactivation volume in the range described above is suitable formanufacturing a magnetic tape exhibiting excellent electromagneticconversion characteristics. The activation volume of the ε-iron oxidepowder is preferably equal to or greater than 300 nm³, and can also be,for example, equal to or greater than 500 nm³. In addition, from aviewpoint of further improving the electromagnetic conversioncharacteristics, the activation volume of the ε-iron oxide powder ismore preferably equal to or smaller than 1,400 nm³, even more preferablyequal to or smaller than 1,300 nm³, still preferably equal to or smallerthan 1,200 nm³, and still more preferably equal to or smaller than 1,100nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regard to this point, in one aspect, σs of the ε-ironoxide powder can be equal to or greater than 8 A×m²/kg and can also beequal to or greater than 12 A×m²/kg. On the other hand, from a viewpointof noise reduction, σs of the ε-iron oxide powder is preferably equal toor smaller than 40 A×m²/kg and more preferably equal to or smaller than35 A×m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed on photographicprinting paper or displayed on a display so that the total magnificationratio of 500,000 to obtain an image of particles configuring the powder.A target particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetic mean of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an aspect in which particles configuring theaggregate are directly in contact with each other, but also includes anaspect in which a binding agent or an additive which will be describedlater is interposed between the particles. A term, particles may be usedfor representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

(1) in a case where the shape of the particle observed in the particleimage described above is a needle shape, a fusiform shape, or a columnarshape (here, a height is greater than a maximum long diameter of abottom surface), the size (particle size) of the particles configuringthe powder is shown as a length of a major axis configuring theparticle, that is, a major axis length,

(2) in a case where the shape of the particle is a planar shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and

(3) in a case where the shape of the particle is a sphere shape, apolyhedron shape, or an unspecified shape, and the major axisconfiguring the particles cannot be specified from the shape, theparticle size is shown as an equivalent circle diameter. The equivalentcircle diameter is a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a minor axis, that is, a minor axis length of the particles ismeasured in the measurement described above, a value of (major axislength/minor axis length) of each particle is obtained, and anarithmetic mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the minoraxis length as the definition of the particle size is a length of aminor axis configuring the particle, in a case of (2), the minor axislength is a thickness or a height, and in a case of (3), the major axisand the minor axis are not distinguished, thus, the value of (major axislength/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average major axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably in a range of 50% to 90% by mass and morepreferably in a range of 60% to 90% by mass with respect to a total massof the magnetic layer. A high filling percentage of the ferromagneticpowder in the magnetic layer is preferable from a viewpoint ofimprovement of recording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic recording medium can be used.As the binding agent, a resin selected from a polyurethane resin, apolyester resin, a polyamide resin, a vinyl chloride resin, an acrylicresin obtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later. For thebinding agent described above, descriptions disclosed in paragraphs 0028to 0031 of JP2010-24113A can be referred to. In addition, the bindingagent may be a radiation curable resin such as an electron beam curableresin. For the radiation curable resin, paragraphs 0044 and 0045 ofJP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent canbe, for example, 10,000 to 200,000 as a weight-average molecular weight.The amount of the binding agent used can be, for example, 1.0 to 30.0parts by mass with respect to 100.0 parts by mass of the ferromagneticpowder.

Curing Agent

In addition, a curing agent can also be used together with the bindingagent. As the curing agent, in one aspect, a thermosetting compoundwhich is a compound in which a curing reaction (crosslinking reaction)proceeds due to heating can be used, and in another aspect, aphotocurable compound in which a curing reaction (crosslinking reaction)proceeds due to light irradiation can be used. At least a part of thecuring agent is included in the magnetic layer in a state of beingreacted (crosslinked) with other components such as the binding agent,by proceeding the curing reaction in the manufacturing step of themagnetic tape. The preferred curing agent is a thermosetting compound,and polyisocyanate is suitable. For the details of polyisocyanate,descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A canbe referred to. The amount of the curing agent can be, for example, 0 to80.0 parts by mass with respect to 100.0 parts by mass of the bindingagent in the magnetic layer forming composition, and is preferably 50.0to 80.0 parts by mass, from a viewpoint of improvement of hardness ofeach layer such as the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, the curing agent described above is used asan example. In addition, examples of the additive included in themagnetic layer include a non-magnetic powder, a lubricant, a dispersingagent, a dispersing assistant, a fungicide, an antistatic agent, and anantioxidant.

As the dispersing agent which can be added to the magnetic layer formingcomposition, a well-known dispersing agent for increasing dispersibilityof a ferromagnetic powder in a carboxy group-containing compound, anitrogen-containing compound, or the like can also be used. For example,the nitrogen-containing compound may be any of primary amine representedby NH₂R, secondary amine represented by NHR₂, and tertiary aminerepresented by NR₃. As described above, R indicates any structureconfiguring the nitrogen-containing compound and a plurality of R may bethe same as each other or different from each other. Thenitrogen-containing compound may be a compound (polymer) having aplurality of repeating structures in a molecule. It is thought that anitrogen-containing portion of the nitrogen-containing compoundfunctioning as an adsorption portion to the surface of the particles ofthe ferromagnetic powder is a reason for the nitrogen-containingcompound to function as the dispersing agent. As the carboxygroup-containing compound, for example, fatty acid of oleic acid can beused. Regarding the carboxy group-containing compound, it is thoughtthat a carboxy group functioning as an adsorption portion to the surfaceof the particles of the ferromagnetic powder is a reason for the carboxygroup-containing compound to function as the dispersing agent. It isalso preferable to use the carboxy group-containing compound and thenitrogen-containing compound in combination. The amount of thesedispersing agent used can be suitably set.

The dispersing agent may be added to a non-magnetic layer formingcomposition. For the dispersing agent which can be added to thenon-magnetic layer forming composition, a description disclosed inparagraph 0061 of JP2012-133837A can be referred to.

As the additive that can added to the magnetic layer, for example, apolyalkyleneimine-based polymer described in JP2016-51493A can also beused. For such a polyalkyleneimine-based polymer, paragraphs 0035 to0077 of JP2016-51493A and examples of JP2016-51493A can be referred to.

As the non-magnetic powder which may be contained in the magnetic layer,non-magnetic powder which can function as an abrasive, non-magneticpowder which can function as a projection formation agent which formsprojections suitably protruded from the surface of the magnetic layer,and the like can be used.

The abrasive is preferably a non-magnetic powder having Mohs hardnessexceeding 8 and more preferably a non-magnetic powder having Mohshardness equal to or greater than 9. A maximum value of Mohs hardness is10. The abrasive can be a powder of an inorganic substance and can alsobe a powder of an organic substance. The abrasive can be a powder of aninorganic or organic oxide or a powder of a carbide. Examples of thecarbide include a boron carbide (for example, B₄C), a titanium carbide(for example, TiC), and the like. In addition, diamond can also be usedas the abrasive. In one embodiment, the abrasive is preferably a powderof an inorganic oxide. Specifically, examples of the inorganic oxideinclude alumina (for example, Al₂O₃), a titanium oxide (for example,TiO₂), a cerium oxide (for example, CeO₂), a zirconium oxide (forexample, ZrO₂), and the like, and alumina is preferable among these. TheMohs hardness of alumina is approximately 9. For details of the aluminapowder, description disclosed in paragraph 0021 of JP2013-229090A canalso be referred to. In addition, a specific surface area can be used asan index of a particle size of the abrasive. It is thought that, as thespecific surface area is large, the particle size of primary particlesof the particles configuring the abrasive is small. As the abrasive, itis preferable to use an abrasive having a specific surface area measuredby a Brunauer-Emmett-Teller (BET) method (hereinafter referred to as a“BET specific surface area”) equal to or greater than 14 m²/g. Inaddition, from a viewpoint of dispersibility, it is preferable to use anabrasive having a BET specific surface area equal to or less than 40m²/g. A content of the abrasive in the magnetic layer is preferably 1.0to 20.0 parts by mass and more preferably 1.0 to 15.0 parts by mass withrespect to 100.0 parts by mass of the ferromagnetic powder. As theabrasive, only one kind of non-magnetic powder can be used or two ormore kinds of non-magnetic powders having different compositions and/orphysical properties (for example, size) can also be used. In a case ofusing two or more kinds of non-magnetic powders as the abrasive, thecontent of the abrasive is a total content of the two or more kinds ofnon-magnetic powders. The same also applies to contents of variouscomponents of the invention and the specification. The abrasive ispreferably subjected to a dispersion process (separate dispersion)separately from the ferromagnetic powder, and more preferably subjectedto a dispersion process (separate dispersion) separately from theprojection formation agent which will be described later. In a case ofpreparing the magnetic layer forming composition, the usage of two ormore kinds of dispersion liquids having different components and/ordispersion conditions as a dispersion liquid of the abrasive(hereinafter, also referred to as an “abrasive solution”) is preferablefor controlling the abrasion property of the magnetic tape.

A dispersing agent can also be used to adjust a dispersion state of thedispersion liquid of the abrasive. As a compound that can function as adispersing agent for increasing the dispersibility of the abrasive, anaromatic hydrocarbon compound having a phenolic hydroxy group can beused. The “phenolic hydroxy group” refers to a hydroxy group directlybonded to an aromatic ring. The aromatic ring contained in the aromatichydrocarbon compound may be a monocyclic ring, a polycyclic structure,or a fused ring. From a viewpoint of improving the dispersibility of theabrasive, an aromatic hydrocarbon compound containing a benzene ring ora naphthalene ring is preferable. In addition, the aromatic hydrocarboncompound may have a substituent other than the phenolic hydroxy group.Examples of the substituent other than the phenolic hydroxy groupinclude a halogen atom, an alkyl group, an alkoxy group, an amino group,an acyl group, a nitro group, a nitroso group, and a hydroxyalkyl group,and a halogen atom, an alkyl group, an alkoxy group, an amino group, anda hydroxyalkyl group are preferable. The number of phenolic hydroxygroups contained in one molecule of the aromatic hydrocarbon compoundmay be one, two, three, or more.

As one preferable aspect of the aromatic hydrocarbon compound having aphenolic hydroxy group, a compound represented by Formula 100 can beused.

[In Formula 100, two of X¹⁰¹ to X¹⁰⁸ are hydroxy groups, and the othersix components each independently represent a hydrogen atom or asubstituent.]

In the compound represented by Formula 100, the substitution positionsof two hydroxy groups (phenolic hydroxy groups) are not particularlylimited.

In Formula 100, two of X¹⁰¹ to X¹⁰⁸ are hydroxy groups (phenolic hydroxygroups), and the other six components are each independently represent ahydrogen atom or a substituent. In addition, among X¹⁰¹ to X¹⁰⁸, all ofthe moieties other than the two hydroxy groups may be hydrogen atoms, orsome or all of them may be substituents. Examples of the substituentinclude the substituents described above. As a substituent other thanthe two hydroxy groups, one or more phenolic hydroxy groups may beincluded. From a viewpoint of improving the dispersibility of theabrasive, it is preferable that the components other than the twohydroxy groups of X¹⁰¹ to X¹⁰⁸ are not phenolic hydroxy groups. That is,the compound represented by Formula 100 is preferablydihydroxynaphthalene or a derivative thereof, and more preferably2,3-dihydroxynaphthalene or a derivative thereof. Examples of preferredsubstituents represented by X¹⁰¹ to X¹⁰⁸ include a halogen atom (forexample, a chlorine atom or a bromine atom), an amino group, an alkylgroup having 1 to 6 (preferably 1 to 4) carbon atoms, and a methoxygroup, and an ethoxy group, an acyl group, a nitro group, a nitrosogroup, and —CH₂OH group.

In addition, for the dispersing agent for improving the dispersibilityof the abrasive, description disclosed in paragraphs 0024 to 0028 ofJP2014-179149A can also be referred to.

The dispersing agent for increasing the dispersibility of the abrasivecan be used, for example, in a case of preparing the abrasive solution(for each abrasive solution in a case of preparing a plurality ofabrasive solutions), in a proportion of 0.5 to 20.0 parts by mass and ispreferably used in a proportion of 1.0 to 10.0 parts by mass withrespect to 100.0 parts by mass of the abrasive.

As one aspect of the projection formation agent, carbon black can beused. An average particle size of the carbon black is preferably in arange of 5 to 200 nm and more preferably in a range of 10 to 150 nm. Inaddition, a BET specific surface area of carbon black is preferablyequal to or greater than 10 m²/g and more preferably equal to or greaterthan 15 m²/g. The BET specific surface area of carbon black ispreferably equal to or less than 50 m²/g and more preferably equal to orless than 40 m²/g, from a viewpoint of ease of improving dispersibility.As the other aspect of the projection formation agent, colloidalparticles can be used. As the colloidal particles, inorganic colloidalparticles are preferable, inorganic oxide colloidal particles are morepreferable, and silica colloid particles (colloidal silica) are evenmore preferred, from a viewpoint of availability. In the presentinvention and the present specification, the “colloidal particles” areparticles which are not precipitated but dispersed to generate acolloidal dispersion, in a case where 1 g of the particles is added to100 mL of at least one organic solvent of methyl ethyl ketone,cyclohexanone, toluene, or ethyl acetate, or a mixed solvent includingtwo or more kinds of the solvent described above at any mixing ratio. Anaverage particle size of the colloidal particles can be, for example, 30to 300 nm and is preferably 40 to 200 nm. A content of the projectionformation agent in the magnetic layer is preferably 0.5 to 4.0 parts bymass and more preferably 0.5 to 3.5 parts by mass with respect to 100.0parts by mass of the ferromagnetic powder. The projection formationagent can be subjected to a dispersion process separately from theferromagnetic powder, and can also be subjected to a dispersion processseparately from the abrasive. In a case of preparing the magnetic layerforming composition, two or more kinds of dispersion liquids havingdifferent components and/or dispersion conditions can also be preparedas a dispersion liquid of the projection formation agent (hereinafter,also referred to as an “projection formation agent liquid”).

In addition, as an aspect of an additive that can be contained in themagnetic layer, a compound having an ammonium salt structure of an alkylester anion represented by Formula 1 can be used.

(In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms, and Z⁺represents an ammonium cation.)

The present inventors consider that the compound described above canfunction as a lubricant. This will be described in detail below.

The lubricant can be broadly divided into a fluid lubricant and aboundary lubricant. The inventors consider that a compound having anammonium salt structure of an alkyl ester anion represented by Formula 1can function as a fluid lubricant. It is considered that the fluidlubricant can play a role of imparting lubricity to the magnetic layerby forming a liquid film on the surface of the magnetic layer by itself.It is surmised that, in order to control the AlFeSil abrasionvalue_(45°) and the standard deviation of the AlFeSil abrasion value, itis desirable that the fluid lubricant forms a liquid film on the surfaceof the magnetic layer. In addition, the more stably the surface of themagnetic layer and the AlFeSil prism can slide in a case of measuringthe AlFeSil abrasion value, the smaller the measured value can be.Regarding the liquid film of the fluid lubricant, from a viewpoint ofenabling more stable sliding, it is considered that it is desirable touse an appropriate amount of the fluid lubricant which forms the liquidfilm on the surface of the magnetic layer. This is because it issurmised that, in a case where the amount of the liquid lubricant whichforms the liquid film on the surface of the magnetic layer is excessive,the surface of the magnetic layer and the AlFeSil prism stick to eachother, and the sliding stability tends to decrease. In addition, it issurmised that, in a case where the amount of the liquid lubricant whichforms the liquid film on the surface of the magnetic layer is excessive,the projection formed on the surface of the magnetic layer by, forexample, the projection formation agent is covered with the liquid film.It is considered that this can also be a factor that decreases thesliding stability.

With respect to the point described above, the compound described abovehas an ammonium salt structure of an alkyl ester anion represented byFormula 1. It is considered that the compound having such a structurecan play an excellent role as the fluid lubricant even in a relativelysmall amount. Therefore, it is considered that including the compounddescribed above in the magnetic layer leads to improving the slidingstability between the surface of the magnetic layer of the magnetic tapeand the AlFeSil prism, and contributes to controlling the AlFeSilabrasion value_(45°) and standard deviation of the AlFeSil abrasionvalue.

Hereinafter, the compound will be further described in detail.

In the invention and the specification, unless otherwise noted, groupsdescribed may have a substituent or may be unsubstituted. In addition,the “number of carbon atoms” of a group having a substituent means thenumber of carbon atoms not including the number of carbon atoms of thesubstituent, unless otherwise noted. In the present invention and thespecification, examples of the substituent include an alkyl group (forexample, an alkyl group having 1 to 6 carbon atoms), a hydroxy group, analkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms),a halogen atom (for example, a fluorine atom, a chlorine atom, a bromineatom, or the like), a cyano group, an amino group, a nitro group, anacyl group, a carboxy group, salt of a carboxy group, a sulfonic acidgroup, and salt of a sulfonic acid group.

Regarding the compound having an ammonium salt structure of the alkylester anion represented by the formula 1, at least a part thereofincluded in the magnetic layer can form a liquid film on the surface ofthe magnetic layer, and another part thereof can be included in themagnetic layer, move to the surface of the magnetic layer and form theliquid film during the sliding with the magnetic head. In addition,still another part thereof can be included in the non-magnetic layerwhich will be described later, and can move to the magnetic layer,further move to the surface of the magnetic layer, and form a liquidfilm. The “alkyl ester anion” can also be referred to as an “alkylcarboxylate anion”.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms. Thefluorinated alkyl group has a structure in which some or all of thehydrogen atoms constituting the alkyl group are substituted with afluorine atom. The alkyl group or fluorinated alkyl group represented byR may have a linear structure, a branched structure, may be a cyclicalkyl group or fluorinated alkyl group, and preferably has a linearstructure. The alkyl group or fluorinated alkyl group represented by Rmay have a substituent, may be unsubstituted, and is preferablyunsubstituted. The alkyl group represented by R can be represented by,for example, C_(n)H_(2n+1)—. Here, n represents an integer of 7 or more.In addition, for example, the fluorinated alkyl group represented by Rmay have a structure in which a part or all of the hydrogen atomsconstituting the alkyl group represented by C_(n)H_(2n+1)— aresubstituted with a fluorine atom. The alkyl group or fluorinated alkylgroup represented by R has 7 or more carbon atoms, preferably 8 or morecarbon atoms, more preferably 9 or more carbon atoms, further preferably10 or more carbon atoms, still preferably 11 or more carbon atoms, stillmore preferably 12 or more carbon atoms, and still even more preferably13 or more carbon atoms. The alkyl group or fluorinated alkyl grouprepresented by R has preferably 20 or less carbon atoms, more preferably19 or less carbon atoms, and even more preferably 18 or less carbonatoms.

In Formula 1, Z⁺ represents an ammonium cation. Specifically, theammonium cation has the following structure. In the present inventionand the present specification, “*” in the formulas that represent a partof the compound represents a bonding position between the structure ofthe part and the adjacent atom.

The nitrogen cation N⁺ of the ammonium cation and the oxygen anion O⁻ inFormula 1 may form a salt bridging group to form the ammonium saltstructure of the alkyl ester anion represented by Formula 1. The factthat the compound having the ammonium salt structure of the alkyl esteranion represented by Formula 1 is contained in the magnetic layer can beconfirmed by performing analysis with respect to the magnetic tape byX-ray photoelectron spectroscopy (electron spectroscopy for chemicalanalysis (ESCA)), infrared spectroscopy (IR), or the like.

In one embodiment, the ammonium cation represented by Z⁺ can be providedby, for example, the nitrogen atom of the nitrogen-containing polymerbecoming a cation. The nitrogen-containing polymer means a polymercontaining a nitrogen atom. In the present invention and the presentspecification, a term “polymer” means to include both a homopolymer anda copolymer. The nitrogen atom can be included as an atom configuring amain chain of the polymer in one aspect, and can be included as an atomconstituting a side chain of the polymer in one aspect.

As one aspect of the nitrogen-containing polymer, polyalkyleneimine canbe used. The polyalkyleneimine is a ring-opening polymer ofalkyleneimine and is a polymer having a plurality of repeating unitsrepresented by Formula 2.

The nitrogen atom N configuring the main chain in Formula 2 can beconverted to a nitrogen cation N⁺ to provide an ammonium cationrepresented by Z⁺ in Formula 1. Then, an ammonium salt structure can beformed with the alkyl ester anion, for example, as follows.

Hereinafter, Formula 2 will be described in more detail.

In Formula 2, R¹ and R² each independently represent a hydrogen atom oran alkyl group, and n1 represents an integer of 2 or more.

Examples of the alkyl group represented by R¹ or R² include an alkylgroup having 1 to 6 carbon atoms, preferably an alkyl group having 1 to3 carbon atoms, more preferably a methyl group or an ethyl group, andeven more preferably a methyl group. The alkyl group represented by R¹or R² is preferably an unsubstituted alkyl group. A combination of R¹and R² in Formula 2 is a form in which one is a hydrogen atom and theother is an alkyl group, a form in which both are hydrogen atoms, and aform in which both are an alkyl group (the same or different alkylgroups), and is preferably a form in which both are hydrogen atoms. Asthe alkyleneimine that provides the polyalkyleneimine, a structure ofthe ring that has the smallest number of carbon atoms is ethyleneimine,and the main chain of the alkyleneimine (ethyleneimine) obtained by ringopening of ethyleneimine has 2 carbon atoms. Accordingly, n1 in Formula2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 orless, 6 or less, or 4 or less. The polyalkyleneimine may be ahomopolymer containing only the same structure as the repeatingstructure represented by Formula 2, or may be a copolymer containing twoor more different structures as the repeating structure represented byFormula 2. A number average molecular weight of the polyalkyleneiminethat can be used to form the compound having the ammonium salt structureof the alkyl ester anion represented by Formula 1 can be, for example,equal to or greater than 200, and is preferably equal to or greater than300, and more preferably equal to or greater than 400. In addition, thenumber average molecular weight of the polyalkyleneimine can be, forexample, equal to or less than 10,000, and is preferably equal to orless than 5,000 and more preferably equal to or less than 2,000.

In the present invention and the present specification, the averagemolecular weight (weight-average molecular weight and number averagemolecular weight) is measured by gel permeation chromatography (GPC) andis a value obtained by performing standard polystyrene conversion.Unless otherwise noted, the average molecular weights shown in theexamples which will be described below are values(polystyrene-equivalent values) obtained by standard polystyreneconversion of the values measured under the following measurementconditions using GPC.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard Column TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three kinds of columns are linked in series)

Eluent: Tetrahydrofuran (THF), including stabilizer(2,6-di-t-butyl-4-methylphenol)

Eluent flow rate: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3% by mass

Sample injection amount: 10 μL

In addition, as the other aspect of the nitrogen-containing polymer,polyallylamine can be used. The polyallylamine is a polymer ofallylamine and is a polymer having a plurality of repeating unitsrepresented by Formula 3.

The nitrogen atom N configuring an amino group of a side chain inFormula 3 can be converted to a nitrogen cation N⁺ to provide anammonium cation represented by Z⁺ in Formula 1. Then, an ammonium saltstructure can be formed with the alkyl ester anion, for example, asfollows.

A weight-average molecular weight of the polyallylamine that can be usedto form the compound having the ammonium salt structure of the alkylester anion represented by Formula 1 can be, for example, equal to orgreater than 200, and is preferably equal to or greater than 1,000, andmore preferably equal to or greater than 1,500. In addition, theweight-average molecular weight of the polyallylamine can be, forexample, equal to or less than 15,000, and is preferably equal to orless than 10,000 and more preferably equal to or less than 8,000.

The fact that the compound having a structure derived frompolyalkyleneimine or polyallylamine as the compound having the ammoniumsalt structure of the alkyl ester anion represented by Formula 1 isincluded can be confirmed by analyzing the surface of the magnetic layerby a time-of-flight secondary ion mass spectrometry (TOF-SIMS) or thelike.

The compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 can be salt of a nitrogen-containing polymerand one or more fatty acids selected from the group consisting of fattyacids having 7 or more carbon atoms and fluorinated fatty acids having 7or more carbon atoms. The nitrogen-containing polymer forming salt canbe one kind or two or more kinds of nitrogen-containing polymers, andcan be, for example, a nitrogen-containing polymer selected from thegroup consisting of polyalkyleneimine and polyallylamine. The fattyacids forming the salt can be one kind or two or more kinds of fattyacids selected from the group consisting of fatty acids having 7 or morecarbon atoms and fluorinated fatty acids having 7 or more carbon atoms.The fluorinated fatty acid has a structure in which some or all of thehydrogen atoms configuring the alkyl group bonded to a carboxy groupCOOH in the fatty acid are substituted with fluorine atoms. For example,the salt forming reaction can easily proceed by mixing thenitrogen-containing polymer and the fatty acids described above at roomtemperature. The room temperature is, for example, approximately 20° C.to 25° C. In one embodiment, one or more kinds of nitrogen-containingpolymers and one or more kinds of the fatty acids described above areused as components of the magnetic layer forming composition, and thesalt forming reaction can proceed by mixing these in the step ofpreparing the magnetic layer forming composition. In one embodiment, oneor more kinds of nitrogen-containing polymers and one or more kinds ofthe fatty acids described above are mixed to form a salt beforepreparing the magnetic layer forming composition, and then, the magneticlayer forming composition can be prepared using this salt as a componentof the magnetic layer forming composition. This point also applies to acase of forming a non-magnetic layer including a compound having anammonium salt structure of an alkyl ester anion represented byFormula 1. For example, for the magnetic layer, 0.1 to 10.0 parts bymass of the nitrogen-containing polymer can be used and 0.5 to 8.0 partsby mass of the nitrogen-containing polymer is preferably used withrespect to 100.0 parts by mass of ferromagnetic powder. The used amountof the fatty acids described above can be, for example, 0.05 to 10.0parts by mass and is preferably 0.1 to 5.0 parts by mass, with respectto 100.0 parts by mass of ferromagnetic powder. In addition, for thenon-magnetic layer, 0.1 to 10.0 parts by mass of the nitrogen-containingpolymer can be used and 0.5 to 8.0 parts by mass of thenitrogen-containing polymer is preferably used with respect to 100.0parts by mass of non-magnetic powder. The used amount of the fatty acidsdescribed above can be, for example, 0.05 to 10.0 parts by mass and ispreferably 0.1 to 5.0 parts by mass, with respect to 100.0 parts by massof non-magnetic powder. In a case where the nitrogen-containing polymerand the fatty acid are mixed to form an ammonium salt of the alkyl esteranion represented by Formula 1, the nitrogen atom configuring thenitrogen-containing polymer and the carboxy group of the fatty acid maybe reacted to form the following structure, and an aspect including suchstructures are also included in the above compound.

Examples of the fatty acids include fatty acids having an alkyl groupdescribed above as R in Formula 1 and fluorinated fatty acids having afluorinated alkyl group described above as R in Formula 1.

A mixing ratio of the nitrogen-containing polymer and the fatty acidused to form the compound having the ammonium salt structure of thealkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10,more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20,as a mass ratio of nitrogen-containing polymer:fatty acid. In addition,the compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 that is contained in the magnetic layer ispreferably 0.01 parts by mass or more, more preferably 0.1 parts bymass, even more preferably 0.5 parts by mass with respect to 100.0 partsby mass of the ferromagnetic powder. Here, a content of the compound inthe magnetic layer means a total amount of the amount of the liquid filmformed on the surface of the magnetic layer and the amount contained inthe magnetic layer. On the other hand, it is preferable that a contentof the ferromagnetic powder in the magnetic layer is high from aviewpoint of high-density recording. Therefore, from a viewpoint ofhigh-density recording, it is preferable that a content of componentsother than the ferromagnetic powder is small. From this viewpoint, thecontent of the compound in the magnetic layer is preferably 15.0 partsby mass or less, more preferably 10.0 parts by mass or less, and evenmore preferably 8.0 parts by mass or less with respect to 100.0 parts bymass of the ferromagnetic powder. In addition, the same applies to thepreferable range of the content of the compound in the magnetic layerforming composition used for forming the magnetic layer.

The magnetic layer may further contain one or more lubricants. As anexample of the lubricant, a fatty acid amide that can function as aboundary lubricant can be used. It is considered that the boundarylubricant is a lubricant which can be adsorbed to a surface of powder(for example, ferromagnetic powder) and form a rigid lubricant film todecrease contact friction. Examples of fatty acid amide include amide ofvarious fatty acids such as lauric acid, myristic acid, palmitic acid,stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid,erucic acid, and elaidic acid, and specifically, lauric acid amide,myristic acid amide, palmitic acid amide, stearic acid amide, and thelike. The content of fatty acid amide in the magnetic layer is, forexample, 0 to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, andmore preferably 0 to 1.0 parts by mass with respect to 100.0 parts bymass of the ferromagnetic powder. In addition, the non-magnetic layermay also contain fatty acid amide. The content of fatty acid amide inthe non-magnetic layer is, for example, 0 to 3.0 parts by mass and ispreferably 0 to 1.0 parts by mass with respect to 100.0 parts by mass ofnon-magnetic powder. For the dispersing agent, a description disclosedin paragraphs 0061 and 0071 of JP2012-133837A can be referred to. Thedispersing agent may be added to a non-magnetic layer formingcomposition. For the dispersing agent which can be added to thenon-magnetic layer forming composition, a description disclosed inparagraph 0061 of JP2012-133837A can be referred to.

Regarding the suppressing of a deterioration in electromagneticconversion characteristics in a case of performing the recording data ona magnetic tape and/or reproducing the recorded data at different headtilt angles, the inventors of the present invention consider as follows.

It is surmised that, in a case where the head tilt angle is different,as described above, a degree of abrasion of the magnetic tape head dueto contact with the magnetic tape head greatly changes during therecording and/or reproducing (large variation occurs in degree ofabrasion). It is considered that the large variation in degree ofabrasion is a factor of a deterioration in electromagnetic conversioncharacteristics.

Meanwhile, it is considered that the abrasion is affected by a size anda content of the abrasive, a shear stress on the magnetic head (whichmay affect the friction properties), a normal force and the like. Sincethe normal force tends to increase as the value of the head tilt angleincreases, it is considered that the abrasive bites into the magnetichead becomes deeper, the friction increases, and the abrasion increases.On the other hand, for example, the use of the compound described above,which is considered to be able to function as a liquid lubricant, as acomponent of the magnetic layer leads to an increase in lubricity(sliding properties) of the surface of the magnetic layer, and cancontribute to suppressing of the occurrence of a large variation indegree of abrasion of the magnetic head due to a difference in head tiltangle. In addition, for the abrasive, it is surmised that the larger theamount of the abrasive contained in the magnetic layer, the more likelythe abrasion of the magnetic head occurs in a case where the head tiltangle is large. In a case where the head tilt angle is small, in a casewhere a plurality of abrasives having different sizes are used ascomponents of the magnetic layer, it is surmised that the abrasiveshaving a larger size are more likely to cause abrasion of the magnetichead.

With respect to the above points, the inventors of the present inventionconsider that, the use of the compound described above as the componentused as the lubricant for forming the magnetic layer, the combination ofthe abrasive used, and/or the adjustment of the content of the abrasivecan contribute to the suppressing of the values of the AlFeSil abrasionvalue_(45°) and the standard deviation of the AlFeSil abrasion value. Inaddition, it is surmised that controlling the values of the AlFeSilabrasion value_(45°) and the standard deviation of the AlFeSil abrasionvalue to be in the ranges described above can lead to the suppressing ofthe deterioration in electromagnetic conversion characteristics in acase of performing the recording and/or reproducing of data on themagnetic tape at different head tilt angles.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the non-magnetic support or mayinclude a non-magnetic layer containing the non-magnetic powder betweenthe non-magnetic support and the magnetic layer. The non-magnetic powderused for the non-magnetic layer may be a powder of an inorganicsubstance (inorganic powder) or a powder of an organic substance(organic powder). In addition, carbon black and the like can be used.Examples of the inorganic substance include metal, metal oxide, metalcarbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide. The non-magnetic powder can be purchased as a commerciallyavailable product or can be manufactured by a well-known method. Fordetails thereof, descriptions disclosed in paragraphs 0146 to 0150 ofJP2011-216149A can be referred to. For carbon black which can be used inthe non-magnetic layer, descriptions disclosed in paragraphs 0040 and0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50% to 90% by mass and more preferably in arange of 60% to 90% by mass with respect to a total mass of thenon-magnetic layer.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent or additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer containing a small amount offerromagnetic powder as impurities, or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heat treatmentmay be performed with respect to these supports in advance.

Back Coating Layer

The tape may or may not include a back coating layer containing anon-magnetic powder on a surface side of the non-magnetic supportopposite to the surface side provided with the magnetic layer. The backcoating layer preferably includes any one or both of carbon black andinorganic powder. The back coating layer can include a binding agent andcan also include additives. For the details of the non-magnetic powder,the binding agent included in the back coating layer and variousadditives, a well-known technology regarding the back coating layer canbe applied, and a well-known technology regarding the magnetic layerand/or the non-magnetic layer can also be applied. For example, for theback coating layer, descriptions disclosed in paragraphs 0018 to 0020 ofJP2006-331625A and page 4, line 65, to page 5, line 38, of U.S. Pat. No.7,029,774B can be referred to.

Various Thicknesses

The tape thickness of the magnetic tape is as described above.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm,preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.7 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and even more preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscopeor a transmission electron microscope. Various thicknesses can beobtained as the arithmetic mean of the thicknesses obtained at tworandom portions in the cross section observation. Alternatively, variousthicknesses can be obtained as a designed thickness calculated under themanufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Composition for forming the magnetic layer, the non-magnetic layer, orthe back coating layer generally includes a solvent, together with thevarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among them, from a viewpoint of thesolubility of the binding agent usually used for the coating typemagnetic recording medium, each layer forming composition preferablycontains one or more of a ketone solvent such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of solvent in each layerforming composition is not particularly limited, and can be identical tothat in each layer forming composition of a typical coating typemagnetic recording medium. In addition, a step of preparing each layerforming composition can generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, as necessary. Each step may be divided into two or more stages.The component used in the preparation of each layer forming compositionmay be added at an initial stage or in a middle stage of each step. Inaddition, each component may be separately added in two or more steps.For example, a binding agent may be separately added in a kneading step,a dispersing step, and a mixing step for adjusting viscosity after thedispersion. In addition, as described above, one or more kinds ofnitrogen-containing polymers and one or more kinds of the fatty acidsdescribed above are used as components of the magnetic layer formingcomposition, and the salt forming reaction can proceed by mixing thesein the step of preparing the magnetic layer forming composition. In oneembodiment, one or more kinds of nitrogen-containing polymers and one ormore kinds of the fatty acids described above are mixed to form a saltbefore preparing the magnetic layer forming composition, and then, themagnetic layer forming composition can be prepared using this salt as acomponent of the magnetic layer forming composition. This point alsoapplies to a step of preparing the non-magnetic layer formingcomposition. The abrasive solution is preferably prepared by dispersingseparately from the ferromagnetic powder and the projection formationagent. The abrasive solution is preferably prepared as one or moreabrasive solutions containing an abrasive, a solvent, and preferably abinding agent, separately from the ferromagnetic powder and theprojection formation agent, and can be used in the preparation of themagnetic layer forming composition. A dispersion process and/or aclassification process can be performed for the preparation of theabrasive solution. A commercially available device can be used for theseprocesses.

In the manufacturing step of the magnetic tape, a well-knownmanufacturing technology of the related art can be used as a part ofstep or the entire step. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. For details ofthe kneading processes, descriptions disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A) can be referred to.In addition, glass beads and/or other beads can be used to disperse eachlayer forming composition. As such dispersion beads, zirconia beads,titania beads, and steel beads which are dispersion beads having highspecific gravity are suitable. These dispersion beads is preferably usedby optimizing a particle diameter (bead diameter) and a fillingpercentage of these dispersion beads. As a disperser, a well-knowndispersion device can be used. Each layer forming composition may befiltered by a well-known method before performing the coating step. Thefiltering can be performed by using a filter, for example. As the filterused in the filtering, a filter having a hole diameter of 0.01 to 3 μm(for example, filter made of glass fiber or filter made ofpolypropylene) can be used, for example.

Regarding the dispersion process of the magnetic layer formingcomposition, in one aspect, the dispersion process of the ferromagneticpowder is performed by the two-stage dispersion process. A coarseaggregate of the ferromagnetic powder is crushed by a first stagedispersion process. After that, a second stage dispersion process inwhich a collision energy applied to the particles of the ferromagneticpowder by the collision with the dispersion beads is smaller than thatin the first dispersion process can be performed. It is considered thatsuch dispersion process makes it possible to improve the dispersibilityof the ferromagnetic powder and prevent the occurrence of chipping(partially lacking particles).

As an example of the two-stage dispersion process described above, adispersion process including a first stage of obtaining a dispersionliquid by performing the dispersion process of a ferromagnetic powder, abinding agent, and a solvent in the presence of first dispersion beads,and a second stage of performing the dispersion process of a dispersionliquid obtained in the first stage in the presence of second dispersionbeads having a bead diameter and a density smaller than those of thefirst dispersion beads. Hereinafter, the dispersion process describedabove will be in detail.

In order to improve the dispersibility of the ferromagnetic powder, itis preferable that the first stage and the second stage described aboveare performed as a dispersion process before mixing the ferromagneticpowder with other powder components. For example, it is preferable toperform the first stage and the second stage as the dispersion processof a liquid (magnetic liquid) containing a ferromagnetic powder, abinding agent, a solvent, and optionally added additives before mixingwith an abrasive and a projection formation agent.

A bead diameter of the second dispersion beads is preferably 1/100 orless, and more preferably 1/500 or less of a bead diameter of the firstdispersion beads. In addition, the bead diameter of the seconddispersion beads can be, for example, 1/10,000 or more of the beaddiameter of the first dispersion beads. However, there is no limitationto this range. For example, the bead diameter of the second dispersionbeads is preferably in a range of 80 to 1,000 nm. Meanwhile, the beaddiameter of the first dispersion beads can be, for example, in a rangeof 0.2 to 1.0 mm

In the present invention and the present specification, the beaddiameter is a value measured by the same method as the method formeasuring the average particle size of powder described above.

The above second stage is preferably performed under the condition inwhich the second dispersion beads are present in an amount of 10 timesor more the amount of the ferromagnetic hexagonal ferrite powder basedon mass, and more preferably performed under the condition in which theamount is 10 to 30 times thereof.

Meanwhile, the amount of the first dispersion beads in the first stageis also preferably in the above range.

The second dispersion beads are beads having a density lower than thatof the first dispersion beads. The “density” is obtained by dividing themass (unit: g) of dispersion beads by the volume (unit: cm³). Themeasurement is performed by the Archimedes method. The density of thesecond dispersion beads is preferably equal to or less than 3.7 g/cm³and more preferably equal to or less than 3.5 g/cm³. The density of thesecond dispersion beads may be, for example, equal to or greater than2.0 g/cm³ or may be less than 2.0 g/cm³. Examples of preferred seconddispersion beads in terms of density include diamond beads, siliconcarbide beads, silicon nitride beads, and the like, and examples ofpreferred second dispersion beads in terms of density and hardnessinclude diamond beads.

On the other hand, the first dispersion beads are preferably dispersionbeads having a density greater than 3.7 g/cm³, more preferablydispersion beads having a density equal to or greater than 3.8 g/cm³,and even more preferably dispersion beads having a density equal to orgreater than 4.0 g/cm³. The density of the first dispersion beads maybe, for example, equal to or less than 7.0 g/cm³ or may be greater than7.0 g/cm³. As the first dispersion beads, zirconia beads, alumina beads,and the like are preferably used, and zirconia beads are more preferablyused.

The dispersion time is not particularly limited and may be set accordingto a type of a disperser used.

Coating Step

The magnetic layer can be formed by, for example, directly applying themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. In an case of performing an alignment process, while the coatinglayer of the magnetic layer forming composition is wet, the alignmentprocess is performed with respect to the coating layer in an alignmentzone. For the alignment process, various technologies disclosed in aparagraph 0052 of JP2010-24113A can be applied. For example, ahomeotropic alignment process can be performed by a well-known methodsuch as a method using a different polar facing magnet. In the alignmentzone, a drying speed of the coating layer can be controlled by atemperature and an air flow of the dry air and/or a transporting rate inthe alignment zone. In addition, the coating layer may be preliminarilydried before transporting to the alignment zone.

The back coating layer can be formed by applying a back coating layerforming composition onto a side of the non-magnetic support opposite tothe side provided with the magnetic layer (or to be provided with themagnetic layer). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

After performing the coating step described above, a calendar process isusually performed in order to improve surface smoothness of the magnetictape. For calendar conditions, a calendar pressure is, for example, 200to 500 kN/m and preferably 250 to 350 kN/m, a calendar temperature(surface temperature of calendar roll) is, for example, 70° C. to 120°C. and preferably 80° C. to 120° C., and a calendar speed is, forexample, 50 to 300 m/min and preferably 80 to 200 m/min. In addition, asa roll having a hard surface is used as a calendar roll, or as thenumber of stages is increased, the surface of the magnetic layer tendsto be smoother.

For various other steps for manufacturing a magnetic tape, a descriptiondisclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referredto.

Through various steps, a long magnetic tape raw material can beobtained. The obtained magnetic tape raw material is, for example, cut(slit) by a well-known cutter to have a width of a magnetic tape to beaccommodated around the magnetic tape cartridge. The width can bedetermined according to the standard and is normally ½ inches. 1inch=2.54 cm.

In the magnetic tape obtained by slitting, normally, a servo pattern canbe formed.

Heat Treatment

In one embodiment, the magnetic tape can be a magnetic tape manufacturedthrough the following heat treatment. In another aspect, the magnetictape can be manufactured without the following heat treatment.

The heat treatment can be performed in a state where the magnetic tapeslit and cut to have a width determined according to the standard iswound around a core member.

In one embodiment, the heat treatment is performed in a state where themagnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a cartridge reel of themagnetic tape cartridge, and a magnetic tape cartridge in which themagnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high stiffness, from a viewpoint of preventing the occurrence ofa winding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for stiffness, a bending elastic modulus of thematerial for the core for heat treatment is preferably equal to orgreater than 0.2 GPa (gigapascal) and more preferably equal to orgreater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the core for heat treatmentof the material having stiffness exceeding the stiffness capable ofpreventing the occurrence of the winding defect causes the costincrease. By considering the viewpoint described above, the bendingelastic modulus of the material for the core for heat treatment ispreferably equal to or smaller than 250 GPa. The bending elastic modulusis a value measured based on international organization forstandardization (ISO) 178 and the bending elastic modulus of variousmaterials is well known. In addition, the core for heat treatment can bea solid or hollow core member. In a case of a hollow shape, a wallthickness is preferably equal to or greater than 2 mm, from a viewpointof maintaining the stiffness. In addition, the core for heat treatmentmay include or may not include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length +α”, from aviewpoint of ease of winding around the core for heat treatment. This ais preferably equal to or greater than 5 m, from a viewpoint of ease ofthe winding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N (newton). Inaddition, from a viewpoint of preventing the occurrence of excessivedeformation during the manufacturing, the tension in a case of windingaround the core for heat treatment is preferably equal to or smallerthan 1.5 N and more preferably equal to or smaller than 1.0 N. An outerdiameter of the core for heat treatment is preferably equal to orgreater than 20 mm and more preferably equal to or greater than 40 mm,from viewpoints of ease of the winding and preventing coiling (curl inlongitudinal direction). The outer diameter of the core for heattreatment is preferably equal to or smaller than 100 mm and morepreferably equal to or smaller than 90 mm A width of the core for heattreatment may be equal to or greater than the width of the magnetic tapewound around this core. In addition, after the heat treatment, in a caseof detaching the magnetic tape from the core for heat treatment, it ispreferable that the magnetic tape and the core for heat treatment aresufficiently cooled and magnetic tape is detached from the core for heattreatment, in order to prevent the occurrence of the tape deformationwhich is not intended during the detaching operation. It is preferablethe detached magnetic tape is wound around another core temporarily(referred to as a “core for temporary winding”), and the magnetic tapeis wound around a cartridge reel (generally, outer diameter isapproximately 40 to 50 mm) of the magnetic tape cartridge from the corefor temporary winding. Accordingly, a relationship between the insideand the outside with respect to the core for heat treatment of themagnetic tape in a case of the heat treatment can be maintained and themagnetic tape can be wound around the cartridge reel of the magnetictape cartridge. Regarding the details of the core for temporary windingand the tension in a case of winding the magnetic tape around the core,the description described above regarding the core for heat treatmentcan be referred to. In an aspect in which the heat treatment issubjected to the magnetic tape having a length of the “final productlength+α”, the length corresponding to “+α” may be cut in any stage. Forexample, in one aspect, the magnetic tape having the final productlength may be wound around the reel of the magnetic tape cartridge fromthe core for temporary winding and the remaining length correspondingthe “+α” may be cut. From a viewpoint of decreasing the amount of theportion to be cut out and removed, the α is preferably equal to orsmaller than 20 m.

The specific aspect of the heat treatment performed in a state of beingwound around the core member as described above is described below.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C., more preferably equal to or lower than70° C., and even more preferably equal to or lower than 65° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Regarding the control of the standard deviation of the curvaturedescribed above, as any value of the heat treatment temperature, heattreatment time, bending elastic modulus of a core for the heattreatment, and tension at the time of winding around the core for theheat treatment is large, the value of the curvature tends to furtherdecrease.

Formation of Servo Pattern

The “formation of the servo pattern” can be “recording of a servosignal”. The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear tape-open (LTO) standard (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. In the invention andthe specification, the “timing-based servo pattern” refers to a servopattern that enables head tracking in a servo system of a timing-basedservo system. As described above, a reason for that the servo pattern isconfigured with one pair of magnetic stripes not parallel to each otheris because a servo signal reading element passing on the servo patternrecognizes a passage position thereof. Specifically, one pair of themagnetic stripes are formed so that a gap thereof is continuouslychanged along the width direction of the magnetic tape, and a relativeposition of the servo pattern and the servo signal reading element canbe recognized, by the reading of the gap thereof by the servo signalreading element. The information of this relative position can realizethe tracking of a data track. Accordingly, a plurality of servo tracksare generally set on the servo pattern along the width direction of themagnetic tape.

The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. A plurality of servo bandsare normally provided on the magnetic tape. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one aspect, as shown in JP2004-318983A, information showing thenumber of servo band (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pair of servo stripes inthe servo band so that the position thereof is relatively deviated inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpair of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes is shifted in the longitudinaldirection of the magnetic tape, in the same manner as the UDIMinformation. However, unlike the UDIM information, the same signal isrecorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-53940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Vertical Squareness Ratio

In one embodiment, the vertical squareness ratio of the magnetic tapecan be, for example, 0.55 or more. From a viewpoint of improving theelectromagnetic conversion characteristics, the vertical squarenessratio of the magnetic tape is preferably 0.60 or more, and morepreferably 0.65 or more. In principle, an upper limit of the squarenessratio is 1.00 or less. The vertical squareness ratio of the magnetictape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 or less, or0.80 or less. It is preferable that the value of the vertical squarenessratio of the magnetic tape is large from a viewpoint of improving theelectromagnetic conversion characteristics. The vertical squarenessratio of the magnetic tape can be controlled by a well-known method suchas performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio”is squareness ratio measured in the vertical direction of the magnetictape. The “vertical direction” described with respect to the squarenessratio is a direction orthogonal to the surface of the magnetic layer,and can also be referred to as a thickness direction. In the inventionand the specification, the vertical squareness ratio is obtained by thefollowing method.

A sample piece having a size that can be introduced into an oscillationsample type magnetic-flux meter is cut out from the magnetic tape to bemeasured. Regarding the sample piece, using the oscillation sample typemagnetic-flux meter, a magnetic field is applied to a vertical directionof a sample piece (direction orthogonal to the surface of the magneticlayer) with a maximum applied magnetic field of 3979 kA/m, a measurementtemperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec,and a magnetization strength of the sample piece with respect to theapplied magnetic field is measured. The measured value of themagnetization strength is obtained as a value after diamagnetic fieldcorrection and a value obtained by subtracting magnetization of a sampleprobe of the oscillation sample type magnetic-flux meter as backgroundnoise. In a case where the magnetization strength at the maximum appliedmagnetic field is Ms and the magnetization strength at zero appliedmagnetic field is Mr, the squareness ratio SQ is a value calculated asSQ=Mr/Ms. The measurement temperature is referred to as a temperature ofthe sample piece, and by setting the ambient temperature around thesample piece to a measurement temperature, the temperature of the samplepiece can be set to the measurement temperature by realizing temperatureequilibrium.

Magnetic Tape Cartridge

According to another aspect of the invention, there is provided amagnetic tape cartridge comprising the magnetic tape described above.

The details of the magnetic tape included in the magnetic tape cartridgeare as described above.

In the magnetic tape cartridge, the magnetic tape is generallyaccommodated in a cartridge main body in a state of being wound around areel. The reel is rotatably provided in the cartridge main body. As themagnetic tape cartridge, a single reel type magnetic tape cartridgeincluding one reel in a cartridge main body and a twin reel typemagnetic tape cartridge including two reels in a cartridge main body arewidely used. In a case where the single reel type magnetic tapecartridge is mounted in the magnetic tape device in order to recordand/or reproduce data on the magnetic tape, the magnetic tape is drawnfrom the magnetic tape cartridge and wound around the reel on themagnetic tape device side. A magnetic head is disposed on a magnetictape transportation path from the magnetic tape cartridge to a windingreel. Feeding and winding of the magnetic tape are performed between areel (supply reel) on the magnetic tape cartridge side and a reel(winding reel) on the magnetic tape device side. In the meantime, forexample, the magnetic head comes into contact with and slides on thesurface of the magnetic layer of the magnetic tape, and accordingly, therecording and/or reproducing of data is performed. With respect to this,in the twin reel type magnetic tape cartridge, both reels of the supplyreel and the winding reel are provided in the magnetic tape cartridge.

In one aspect, the magnetic tape cartridge can include a cartridgememory. The cartridge memory can be, for example, a non-volatile memory,and head tilt angle adjustment information is recorded in advance orhead tilt angle adjustment information is recorded. The head tilt angleadjustment information is information for adjusting the head tilt angleduring the running of the magnetic tape in the magnetic tape device. Forexample, as the head tilt angle adjustment information, a value of theservo band spacing at each position in the longitudinal direction of themagnetic tape at the time of data recording can be recorded. Forexample, in a case where the data recorded on the magnetic tape isreproduced, the value of the servo band spacing is measured at the timeof the reproducing, and the head tilt angle θ can be changed by thecontrol device of the magnetic tape device so that an absolute value ofa difference of the servo band spacing at the time of recording at thesame longitudinal position recorded in the cartridge memory is close to0. The head tilt angle can be, for example, the angle θ described above.

The magnetic tape and the magnetic tape cartridge can be suitably usedin the magnetic tape device (that is, magnetic recording and reproducingsystem) for performing recording and/or reproducing data at differenthead tilt angles. In such a magnetic tape device, in one embodiment, itis possible to perform the recording and/or reproducing of data bychanging the head tilt angle during running of a magnetic tape. Forexample, the head tilt angle can be changed according to dimensionalinformation of the magnetic tape in the width direction obtained whilethe magnetic tape is running. In addition, for example, in a usageaspect, a head tilt angle during the recording and/or reproducing at acertain time and a head tilt angle during the recording and/orreproducing at the next time and subsequent times are changed, and thenthe head tilt angle may be fixed without changing during the running ofthe magnetic tape for the recording and/or reproducing of each time. Inany usage aspect, a magnetic tape having a small deterioration inelectromagnetic conversion characteristics in a case of performing therecording and/or reproducing of data at different head tilt angles ispreferable.

Magnetic Tape Device

According to still another aspect of the invention, there is provided amagnetic tape device comprising the magnetic tape described above. Inthe magnetic tape device, the recording of data on the magnetic tapeand/or the reproducing of data recorded on the magnetic tape can beperformed by bringing the surface of the magnetic layer of the magnetictape into contact with the magnetic head and sliding. The magnetic tapedevice can attachably and detachably include the magnetic tape cartridgeaccording to one aspect of the invention.

The magnetic tape cartridge can be attached to a magnetic tape deviceprovided with a magnetic head and used for performing the recordingand/or reproducing of data. In the invention and the specification, the“magnetic tape device” means a device capable of performing at least oneof the recording of data on the magnetic tape or the reproducing of datarecorded on the magnetic tape. Such a device is generally called adrive.

Magnetic Head

The magnetic tape device can include a magnetic head. The configurationof the magnetic head and the angle θ, which is the head tilt angle, areas described above with reference to FIGS. 1 to 3 . In a case where themagnetic head includes a reproducing element, as the reproducingelement, a magnetoresistive (MR) element capable of reading informationrecorded on the magnetic tape with excellent sensitivity is preferable.As the MR element, various well-known MR elements (for example, a GiantMagnetoresistive (GMR) element, or a Tunnel Magnetoresistive (TMR)element) can be used. Hereinafter, the magnetic head which records dataand/or reproduces the recorded data is also referred to as a “recordingand reproducing head”. The element for recording data (recordingelement) and the element for reproducing data (reproducing element) arecollectively referred to as a “magnetic head element”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.3 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,tracking using a servo signal can be performed. That is, as the servosignal reading element follows a predetermined servo track, the magnetichead element can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. InFIG. 5 , a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape MT. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 6 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 6 , a servo frameSF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) anda servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with anA burst (in FIG. 6 , reference numeral A) and a B burst (in FIG. 6 ,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 6, reference numeral C) and a D burst (in FIG. 6 , reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for recognizingthe servo frames. FIG. 6 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking servo in the timing-based servo system is performed, aplurality of servo frames are disposed in each servo band in a runningdirection. In FIG. 6 , an arrow shows a magnetic tape running direction.For example, an LTO Ultrium format tape generally includes 5,000 or moreservo frames per a tape length of 1 m, in each servo band of themagnetic layer.

In the magnetic tape device, the head tilt angle can be changed whilethe magnetic tape is running in the magnetic tape device. The head tiltangle is, for example, an angle θ formed by the axis of the elementarray with respect to the width direction of the magnetic tape. Theangle θ is as described above. For example, by providing an angleadjustment unit for adjusting the angle of the module of the magnetichead in the recording and reproducing head unit of the magnetic head,the angle θ can be variably adjusted during the running of the magnetictape. Such an angle adjustment unit can include, for example, a rotationmechanism for rotating the module. For the angle adjustment unit, awell-known technology can be applied.

Regarding the head tilt angle during the running of the magnetic tape,in a case where the magnetic head includes a plurality of modules, theangle θ described with reference to FIGS. 1 to 3 can be specified forthe randomly selected module. The angle θ at the start of running of themagnetic tape, θ_(initial), can be set to 0° or more or more than 0°. Asthe θ_(initial) is large, a change amount of the effective distancebetween the servo signal reading elements with respect to a changeamount of the angle θ increases, and accordingly, it is preferable froma viewpoint of adjustment ability for adjusting the effective distancebetween the servo signal reading elements according to the dimensionchange of the width direction of the magnetic tape. From this viewpoint,the θ_(initial) is preferably 1° or more, more preferably 5° or more,and even more preferably 10° or more. Meanwhile, regarding an angle(generally referred to as a “lap angle”) formed by a surface of themagnetic layer and a contact surface of the magnetic head in a casewhere the magnetic tape runs and comes into contact with the magnetichead, a deviation in a tape width direction which is kept small iseffective in improving uniformity of friction in the tape widthdirection which is generated by the contact between the magnetic headand the magnetic tape during the running of the magnetic tape. Inaddition, it is desirable to improve the uniformity of the friction inthe tape width direction from a viewpoint of position followability andthe running stability of the magnetic head. From a viewpoint of reducingthe deviation of the lap angle in the tape width direction, θ_(initial)is preferably 45° or less, more preferably 40° or less, and even morepreferably 35° or less.

Regarding the change of the angle θ during the running of the magnetictape, while the magnetic tape is running in the magnetic tape device inorder to record data on the magnetic tape and/or to reproduce datarecorded on the magnetic tape, in a case where the angle θ of themagnetic head changes from θ_(initial) at the start of running, amaximum change amount Δθ of the angle θ during the running of themagnetic tape is a larger value among Δθ_(max) and Δθ_(min) calculatedby the following equation. A maximum value of the angle θ during therunning of the magnetic tape is θ_(max), and a minimum value thereof isθ_(min). In addition, “max” is an abbreviation for maximum, and “min” isan abbreviation for minimum.Δθ_(max)=θ_(max)−θ_(initial) andΔθ_(min)=θ_(initial)−θ_(min).

In one embodiment, the Δθ can be more than 0.000°, and is preferably0.001° or more and more preferably 0.010° or more, from a viewpoint ofadjustment ability for adjusting the effective distance between theservo signal reading elements according to the dimension change in thewidth direction of the magnetic tape. In addition, from a viewpoint ofease of ensuring synchronization of recorded data and/or reproduced databetween a plurality of magnetic head elements during data recordingand/or reproducing, the Δθ is preferably 1.000° or less, more preferably0.900° or less, even more preferably 0.800° or less, still preferably0.700° or less, and still more preferably 0.600° or less.

In the examples shown in FIGS. 2 and 3 , the axis of the element arrayis tilted toward a magnetic tape running direction. However, the presentinvention is not limited to such an example. The present invention alsoincludes an aspect in which the axis of the element array is tilted in adirection opposite to the magnetic tape running direction in themagnetic tape device.

The head tilt angle θ_(initial) at the start of the running of themagnetic tape can be set by a control device or the like of the magnetictape device.

Regarding the head tilt angle during the running of the magnetic tape,FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape. The angle θ during the runningof the magnetic tape can be obtained, for example, by the followingmethod. In a case where the angle θ during traveling on the magnetictape is obtained by the following method, the angle θ is changed in arange of 0° to 90° during the running of the magnetic tape. That is, ina case where the axis of the element array is tilted toward the magnetictape running direction at the start of running of the magnetic tape, theelement array is not tilted so that the axis of the element array tiltstoward a direction opposite to the magnetic tape running direction atthe start of the running of the magnetic tape, during the running of themagnetic tape, and in a case where the axis of the element array istilted toward the direction opposite to the magnetic tape runningdirection at the start of running of the magnetic tape, the elementarray is not tilted so that the axis of the element array tilts towardthe magnetic tape running direction at the start of the running of themagnetic tape, during the running of the magnetic tape.

A phase difference (that is, time difference) ΔT of reproduction signalsof the pair of servo signal reading elements 1 and 2 is measured. Themeasurement of ΔT can be performed by a measurement unit provided in themagnetic tape device. A configuration of such a measurement unit is wellknown. A distance L between a central portion of the servo signalreading element 1 and a central portion of the servo signal readingelement 2 can be measured with an optical microscope or the like. In acase where a running speed of the magnetic tape is defined as a speed v,the distance in the magnetic tape running direction between the centralportions of the two servo signal reading elements is set to L sin θ, anda relationship of L sin θ=v×ΔT is satisfied. Therefore, the angle θduring the running of the magnetic tape can be calculated by a formula“θ=arcsin(vΔT/L)”. The right drawing of FIG. 7 shows an example in whichthe axis of the element array is tilted toward the magnetic tape runningdirection. In this example, the phase difference (that is, timedifference) ΔT of a phase of the reproduction signal of the servo signalreading element 2 with respect to a phase of the reproduction signal ofthe servo signal reading element 1 is measured. In a case where the axisof the element array is tilted toward the direction opposite to therunning direction of the magnetic tape, θ can be obtained by the methoddescribed above, except for measuring ΔT as the phase difference (thatis, time difference) of the phase of the reproduction signal of theservo signal reading element 1 with respect to the phase of thereproduction signal of the servo signal reading element 2.

For a measurement pitch of the angle θ, that is, a measurement intervalof the angle θ in a tape longitudinal direction, a suitable pitch can beselected according to a frequency of tape width deformation in the tapelongitudinal direction. As an example, the measurement pitch can be, forexample, 250 μm.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 8 controls a recording andreproducing head unit 12 in accordance with a command from a controldevice 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting andadjusting a tension applied in a longitudinal direction of the magnetictape from spindle motors 17A and 17B and driving devices 18A and 18Bwhich rotatably control a magnetic tape cartridge reel and a windingreel.

The magnetic tape device 10 has a configuration in which the magnetictape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and writedevice 14 capable of performing reading and writing with respect to thecartridge memory 131 in the magnetic tape cartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled outfrom the magnetic tape cartridge 13 mounted on the magnetic tape device10 by an automatic loading mechanism or manually and passes on arecording and reproducing head through guide rollers 15A and 15B so thata surface of a magnetic layer of the magnetic tape MT comes into contactwith a surface of the recording and reproducing head of the recordingand reproducing head unit 12, and accordingly, the magnetic tape MT iswound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor17B are controlled by a signal from the control device 11, and themagnetic tape MT runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed and control the head tilt angle. A tension detection mechanism maybe provided between the magnetic tape cartridge 13 and the winding reel16 to detect the tension. The tension may be controlled by using theguide rollers 15A and 15B in addition to the control by the spindlemotors 17A and 17B.

The cartridge memory read and write device 14 is configured to be ableto read and write information of the cartridge memory 131 according tocommands from the control device 11. As a communication system betweenthe cartridge memory read and write device 14 and the cartridge memory131, for example, an international organization for standardization(ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 19, a connectorcable for connecting to the control device 11. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able torecord data on the magnetic tape MT according to a command from thecontrol device 11. In addition, the data recorded on the magnetic tapeMT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape MT and position the recording element and/or the reproducingelement at a target running position (track position). The control ofthe track position is performed by feedback control, for example. Thecontrol device 11 has a mechanism of obtaining a servo band spacing fromservo signals read from two adjacent servo bands during the running ofthe magnetic tape MT. The control device 11 can store the obtainedinformation of the servo band spacing in the storage unit inside thecontrol device 11, the cartridge memory 131, an external connectiondevice, and the like. In addition, the control device 11 can change thehead tilt angle according to the dimensional information in the widthdirection of the magnetic tape during the running. Accordingly, it ispossible to bring the effective distance between the servo signalreading elements closer to or match the spacing of the servo bands. Thedimensional information can be obtained by using the servo patternpreviously formed on the magnetic tape. For example, by doing so, theangle θ formed by the axis of the element array with respect to thewidth direction of the magnetic tape can be changed during the runningof the magnetic tape in the magnetic tape device according todimensional information of the magnetic tape in the width directionobtained during the running. The head tilt angle can be adjusted, forexample, by feedback control. Alternatively, for example, the head tiltangle can also be adjusted by a method disclosed in JP2016-524774A orUS2019/0164573A1.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to the embodiments shown in theexamples. “Parts” and “%” in the following description mean “parts bymass” and “mass %”, unless otherwise noted. Steps and evaluationsdescribed below are performed in an environment of an atmospheretemperature of 23° C.±1° C., unless otherwise noted. Further, “eq”described below indicates an equivalent which is a unit which cannot beconverted into the SI unit system.

Ferromagnetic Powder

In Table 2, “BaFe” is a hexagonal barium ferrite powder having anaverage particle size (average plate diameter) of 21 nm.

In Table 2, “SrFe1” is a hexagonal strontium ferrite powder produced bythe following method.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,390° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A×m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKα ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 2, “SrFe2” is a hexagonal strontium ferrite powder produced bythe following method.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,380° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A×m²/kg.

In Table 2, “ε-iron oxide” is an ε-iron oxide powder produced by thefollowing method.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. A citric acid aqueous solution obtainedby dissolving 1 g of citric acid in 9 g of pure water was added to theobtained solution and stirred for 1 hour. The powder precipitated afterthe stirring was collected by centrifugal separation, washed with purewater, and dried in a heating furnace at a furnace inner temperature of80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas disclosed regarding SrFe1 above, and it was confirmed that theobtained ferromagnetic powder has a crystal structure of a single phasewhich is an ε phase not including a crystal structure of an α phase anda γ phase (ε-iron oxide type crystal structure) from the peak of theX-ray diffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle sizewas 12 nm, an activation volume was 746 nm³, an anisotropy constant Kuwas 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

The mass magnetization σs is a value measured using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.) at a magnetic field strength of 15 kOe.

Preparation of Abrasive Solution

Preparation of Abrasive Solution A

The amount of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.) shown in Table 1, 31.3 parts of a 32% solution(solvent is a mixed solvent of methyl ethyl ketone and toluene) of acontaining polyester polyurethane resin having an SO₃Na group as a polargroup (UR-4800 (polar group amount: 80 meq/kg) manufactured by ToyoboCo., Ltd.), and 570.0 parts of a mixed liquid of methyl ethyl ketone andcyclohexanone (mass ratio of 1:1) as a solvent were mixed with respectto 100.0 parts of abrasive (alumina powder) shown in Table 1, anddispersed in the presence of zirconia beads (bead diameter: 0.1 mm) by apaint shaker for the time shown in Table 1 (bead dispersion time).

After the dispersion, the dispersion liquid obtained by separating thedispersion liquid and the beads with a mesh was subjected to acentrifugal separation process. The centrifugal separation process wasperformed by using CS150GXL manufactured by Hitachi Koki Co., Ltd. (arotor used is S100AT6 manufactured by Hitachi Koki Co., Ltd.) as acentrifugal separator for the time (centrifugal separation time) shownin Table 1 at a rotation speed (rpm; rotation per minute) shown inTable 1. By this centrifugal separation process, particles having arelatively large particle size are precipitated, and particles having arelatively small particle size are dispersed in a supernatant.

Then, the supernatant was collected by decantation. This collectedliquid is referred to as an “abrasive solution A”.

Preparation of Abrasive Solutions B and C

An abrasive solution B and an abrasive solution C were prepared in thesame manner as in the preparation of the abrasive solution A, exceptthat various items were changed as shown in Table 1.

TABLE 1 Abrasive Abrasive Abrasive solution A solution B solution CPreparation Abrasive product name Hit80 Hit70 Hit70 of abrasive(manufactured by solution Sumitomo Chemical Co., Ltd.) BET specificsurface 30 20 20 area of abrasive (m²/g) Content of abrasive 3.0 parts3.0 parts 0 parts liquid dispersing agent by mass by mass by mass(2,3-dihydroxy- naphthalene) Beads dispersion time 360 min 180 min 60min Centrifugal Rotation rate 5500 rpm 3500 rpm 1000 rpm separationCentrifugal  4 min  4 min  4 min separation time

Example A1

Preparation of Magnetic Layer Forming Composition

Magnetic Liquid

Ferromagnetic powder (see Table 2): 100.0 parts

Oleic acid: 2.0 parts

Vinyl chloride copolymer (MR-104 manufactured by ZEON CORPORATION): 10.0parts

SO₃Na group-containing polyurethane resin: 4.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group content: 0.07meq/g)

Polyalkyleneimine-based polymer (synthetic product obtained by themethod disclosed in paragraphs 0115 to 0123 of JP2016-51493A): 6.0 parts

Methyl ethyl ketone: 150.0 parts

Cyclohexanone: 150.0 parts

Abrasive Solution

The abrasive solution shown in Table 2 is used with the amount ofabrasive in the abrasive solution shown in Table 2.

Other Components

Carbon black (average particle size: 20 nm): 0.7 part

Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., numberaverage molecular weight: 300): 2.0 parts

Stearic acid: 0.5 parts

Stearic acid amide: 0.3 parts

Butyl stearate: 6.0 parts

Methyl ethyl ketone: 110.0 parts

Cyclohexanone: 110.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 3.0 parts

Preparation Method

A dispersion liquid A was prepared by dispersing (first stage) variouscomponents of the magnetic liquid described above with a batch typevertical sand mill by using zirconia beads having a bead diameter of 0.5mm (first dispersion beads, density of 6.0 g/cm³) for 24 hours, and thenperforming filtering with a filter having a hole diameter of 0.5 μm. Thezirconia beads were used in an amount of 10 times the mass of theferromagnetic powder based on mass.

Then, the dispersion liquid A was dispersed by a batch type verticalsand mill for 1 hour using diamond beads having a bead diameter of 500nm (second dispersion beads, density of 3.5 g/cm³) (second stage), and adispersion liquid (dispersion liquid B) in which diamond beads wereseparated was prepared using a centrifugal separator. The diamond beadswere used in an amount of 10 times the mass of the ferromagnetic powderbased on mass.

The dispersion liquid B, the abrasive solution, and the other componentsdescribed above were introduced into a dissolver stirrer, and stirred ata circumferential speed of 10 m/sec for 360 minutes. Then, afterperforming ultrasonic dispersion process for 60 minutes with a flow typeultrasonic disperser at a flow rate of 7.5 kg/min, the magnetic layerforming composition was prepared by filtering three times with a filterhaving a hole diameter of 0.3 μm.

Preparation of Non-Magnetic Layer Forming Composition

A non-magnetic layer forming composition was prepared by dispersingvarious components of the non-magnetic layer forming compositiondescribed below with a batch type vertical sand mill by using zirconiabeads having a bead diameter of 0.1 mm for 24 hours, and then performingfiltering with a filter having a hole diameter of 0.5 μm.

Non-Magnetic Inorganic Powder

α-iron oxide: 100.0 parts

(Average particle size: 10 nm, BET specific surface area: 75 m²/g)

Carbon black: 25.0 parts

(Average particle size: 20 nm)

SO₃Na group-containing polyurethane resin: 18.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group content: 0.2meq/g)

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

Preparation of Back Coating Layer Forming Composition

Components except a lubricant (stearic acid and butyl stearate),polyisocyanate, and 200.0 parts of cyclohexanone among variouscomponents of the back coating layer forming composition were kneadedand diluted by an open kneader, and subjected to a dispersion process of12 passes, with a transverse beads mill disperser and zirconia beadshaving a bead diameter of 1 mm, by setting a bead filling percentage as80 volume %, a circumferential speed of rotor distal end as 10 m/sec,and a retention time for 1 pass as 2 minutes. After that, the remainingcomponents were added and stirred with a dissolver, the obtaineddispersion liquid was filtered with a filter having a hole diameter of 1μm and a back coating layer forming composition was prepared.

Non-Magnetic Inorganic Powder

α-iron oxide: 80.0 parts

(Average particle size: 0.15 μm, BET specific surface area: 52 m²/g)

Carbon black: 20.0 parts

(Average particle size: 20 nm)

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid salt group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 155.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 200.0 parts

Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition prepared in the section wasapplied to a surface of a support made of polyethylene naphthalatehaving a thickness shown in Table 2 so that the thickness after thedrying becomes a thickness shown in Table 2 and was dried to form anon-magnetic layer.

Then, the magnetic layer forming composition prepared as described abovewas applied onto the non-magnetic layer so that the thickness after thedrying is a thickness shown in Table 2, and a coating layer was formed.

After that, a homeotropic alignment process was performed by applying amagnetic field having a magnetic field strength of 0.3 T in a verticaldirection with respect to a surface of a coating layer, while thecoating layer of the magnetic layer forming composition is wet. Then,the drying was performed to form the magnetic layer.

After that, the back coating layer forming composition prepared asdescribed above was applied to the surface of the support on a sideopposite to the surface where the non-magnetic layer and the magneticlayer were formed, so that the thickness after the drying becomes athickness shown in Table 2, and was dried to form a back coating layer.

After that, a surface smoothing treatment (calender process) wasperformed by using a calender roll configured of only a metal roll, at aspeed of 100 m/min, linear pressure of 300 kg/cm), and a calendertemperature (surface temperature of a calender roll) of 90° C. By doingso, a long magnetic tape raw material was obtained.

Then, after the heat treatment for 36 hours in an environment of anatmosphere temperature of 70° C., a long magnetic tape raw material wasslit into a ½ inches width to obtain a magnetic tape.

By recording a servo signal on a magnetic layer of the obtained magnetictape with a commercially available servo writer, and including a servopattern (timing-based servo pattern) having the disposition and shapeaccording to the linear tape-open (LTO) Ultrium format on the servo bandwas obtained.

Accordingly, a magnetic tape including data bands, servo bands, andguide bands in the disposition according to the LTO Ultrium format inthe magnetic layer, and including servo patterns (timing-based servopattern) having the disposition and the shape according to the LTOUltrium format on the servo band was obtained. The servo pattern formedby doing so is a servo pattern disclosed in Japanese IndustrialStandards (JIS) X6175:2006 and Standard ECMA-319 (June 2001).

The total number of servo bands is five, and the total number of databands is four.

A magnetic tape (length of 960 m) on which the servo signal was recordedas described above was wound around the reel of the magnetic tapecartridge (LTO Ultrium 8 data cartridge), and a leader tape according toArticle 9 of Section 3 of standard European Computer ManufacturersAssociation (ECMA)-319 (June 2001) was bonded to an end thereof by usinga commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

It can be confirmed by the following method that the magnetic layer ofthe magnetic tape contains a compound formed of polyethyleneimine andstearic acid and having an ammonium salt structure of an alkyl esteranion represented by Formula 1.

A sample is cut out from a magnetic tape, and X-ray photoelectronspectroscopy analysis is performed on the surface of the magnetic layer(measurement area: 300 μm×700 μm) using an ESCA device. Specifically,wide scan measurement is performed by the ESCA device under thefollowing measurement conditions. In the measurement results, peaks areconfirmed at a position of a binding energy of the ester anion and aposition of a binding energy of the ammonium cation.

Device: AXIS-ULTRA manufactured by Shimadzu Corporation

Excited X-ray source: Monochromatic Al—Kα ray

Scan range: 0 to 1,200 eV

Pass energy: 160 eV

Energy resolution: 1 eV/step

Capturing Time: 100 ms/step

Number of times of integration: 5

In addition, a sample piece having a length of 3 cm is cut out from themagnetic tape, and attenuated total reflection-fouriertransform-infrared spectrum (ATR-FT-IR) measurement (reflection method)is performed on the surface of the magnetic layer, and, in themeasurement result, the absorption is confirmed on a wave numbercorresponding to absorption of COO⁻ (1,540 cm⁻¹ or 1,430 cm⁻¹) and awave number corresponding to the absorption of the ammonium cation(2,400 cm⁻¹).

Example A2 to Example A22 and Example B1 to Example B28

A magnetic tape and a magnetic tape cartridge were obtained by themethod described in Example A1, except that the items shown in Table 2were changed as shown in Table 2.

For Examples A19 to A22 and Comparative Examples B25 to B28, the stepafter recording the servo signal was changed as follows. That is, theheat treatment was performed after recording the servo signal. On theother hand, in other examples, since such heat treatment was notperformed, “None” was shown in the column of “core for the heattreatment” in Table 2.

For Examples A19 to A22 and Comparative Examples B25 to B28, themagnetic tape (length of 970 m) after recording the servo signal asdescribed in Example Al was wound around a core for the heat treatmentand heat-treated in a state of being wound around the core. As the corefor heat treatment, a solid core member (outer diameter: 50 mm) formedof a resin and having a value of a bending elastic modulus shown inTable 2 was used, and the tension in a case of the winding was set as avalue shown in Table 2. The heat treatment temperature and heattreatment time in the heat treatment were set to values shown in Table2. The weight absolute humidity in the atmosphere in which the heattreatment was performed was 10 g/kg Dry air.

After the heat treatment, the magnetic tape and the core for heattreatment were sufficiently cooled, the magnetic tape was detached fromthe core for heat treatment and wound around the core for temporarywinding, and then, the magnetic tape having the final product length(960 m) was wound around the reel of the magnetic tape cartridge (LTOUltrium 8 data cartridge) from the core for temporary winding. Theremaining length of 10 m was cut out and the leader tape based onsection 9 of Standard European Computer Manufacturers Association(ECMA)-319 (June 2001) Section 3 was bonded to the end of the cut sideby using a commercially available splicing tape.

As the core for temporary winding, a solid core member having the sameouter diameter and formed of the same material as the core for heattreatment was used, and the tension at the time of winding was set as0.6 N.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

For each example, four magnetic tape cartridges were manufactured, onewas used for the evaluation of the deterioration in electromagneticconversion characteristics below, and the other three were used for theevaluations (1) to (3) of the magnetic tape.

Evaluation regarding Deterioration in Electromagnetic ConversionCharacteristics (Reduction Amount of Signal-to-Noise Ratio (SNR))

The reduction amount of SNR was obtained as the evaluation regarding thedeterioration in electromagnetic conversion characteristics by thefollowing method. The following recording and reproducing were performedusing a ½ inch reel tester with a fixed magnetic head, and performedfour times in total by changing the head tilt angle sequentially in theorder of 0°, 15°, 30°, and 45°. The head tilt angle is an angle θ formedby the axis of the element array of the reproducing module describebelow with respect to the width direction of the magnetic tape at thestart of each time of running. The angle θ was set by the control deviceof the magnetic tape device at the start of each time of running of themagnetic tape, and the head tilt angle was fixed during each time ofrunning of the magnetic tape.

For each magnetic tape (total length of magnetic tape: 960 m) of eachexample, in the environment with a temperature of 23° C. and a relativehumidity of 50%, 1000 passes of the recording and reproducing wereperformed by applying a tension of 1.5 N (hereinafter, referred to as a“running tension”) in the longitudinal direction of the magnetic tape,and then 1000 passes of the recording and reproducing were performed byapplying a tension of 0.2 N in the longitudinal direction of themagnetic tape. a relative speed of the magnetic tape and the magnetichead is 8 m/sec, and in the magnetic head used, the arrangement order ofthe modules is “recording module-reproducing module-recording module”(total number of modules: 3). The number of magnetic head elements ineach module is 32 (Ch0 to Ch31), and the element array is configured bysandwiching these magnetic head elements between the pair of servosignal reading elements. The recording element of the recording moduleis a Metal-in-gap (MIG) element (gap length of 0.15 μm, track width of1.0 μm), and the recording is performed by setting a recording currentto an optimum recording current of each magnetic tape. The reproducingelement of the reproducing module is a giant-magnetoresistive (GMR)element (element thickness of 15 nm, shield interval of 0.1 μm,reproducing element width of 0.8 μm). A signal having a linear recordingdensity of 300 kfci was recorded, and the reproduction signal wasmeasured with a spectrum analyzer manufactured by ShibaSoku Co., Ltd. Inaddition, the unit kfci is a unit of linear recording density (cannot beconverted to SI unit system). As the signal, a sufficiently stabilizedportion of the signal after starting the running of the magnetic tapewas used.

At each time, a difference between a SNR of a first pass at a runningtension of 1.5 N and a SNR of a 1000th pass at a running tension of 0.2N (SNR of the 1000th pass at the running tension of 0.2 N—SNR of firstpass at the running tension of 1.5 N) was calculated and set to the SNRreduction amount. An arithmetic average of the SNR reduction amountobtained for the four different head tilt angles is shown in a column of“SNR reduction amount” in Table 2.

Recording Capacity

In each example, even in a case where the tape thickness of the magnetictape is different, the magnetic tape having the same length wasaccommodated in the magnetic tape cartridge.

On the other hand, since the magnetic tape cartridge generallyaccommodates the magnetic tape in a state of being wound around a reelin a housing, it cannot accommodate the magnetic tape having a volumeexceeding the volume in the housing. As the tape thickness of themagnetic tape is large, the tape volume per unit length furtherincreases, and accordingly, a maximum tape length that can beaccommodated in the housing is short.

Regarding the recording capacity, as the magnetic tape having a longertape length is accommodated in one reel of the magnetic tape cartridge,the recording capacity per one reel of the magnetic tape cartridge canbe further increased.

From the above description, a magnetic tape having a longer maximum tapelength that can be accommodated in the housing having a certain volumeis more preferable for high capacity, and such a maximum tape lengthdecreases, as the tape thickness of the magnetic tape is large.Accordingly, the recording capacity of the magnetic tapes of each of theabove examples was evaluated as follows.

The magnetic tape of Example B11 having a tape thickness of 5.6 μm isused as a standard for recording capacity (following evaluationindicator: 100).

For a magnetic tape having a tape thickness of T μm, the evaluationindicator (no unit) of the recording capacity is calculated as“evaluation indicator=(5.6−T)/5.6×100+100”. It can be said that amagnetic tape in which the value calculated as described above is largeis more preferable for high capacity.

Evaluation of Magnetic Tape

(1) AlFeSil Abrasion Value_(45°) and Standard Deviation of AlFeSilAbrasion Value

The magnetic tape was extracted from the magnetic tape cartridges ofeach of examples, and the AlFeSil abrasion value_(45°) and the standarddeviation of the AlFeSil abrasion value were obtained by the methoddescribed above in the environment with the temperature of 23° C. andthe relative humidity of 50%.

(2) Standard Deviation of Curvature of Magnetic Tape in LongitudinalDirection

The magnetic tape was taken out from the magnetic tape cartridge of eachexample, and the standard deviation of the curvature of the magnetictape in the longitudinal direction was determined by the methoddescribed above.

(3) Tape Thickness

10 tape samples (length: 5 cm) were cut out from any part of themagnetic tape taken out from the magnetic tape cartridge of eachexample, and these tape samples were stacked to measure the thickness.The thickness was measured using a digital thickness gauge of a Millimar1240 compact amplifier manufactured by MARH and a Millimar 1301induction probe. The value (thickness per tape sample) obtained bycalculating 1/10 of the measured thickness was defined as the tapethickness.

The result described above is shown in Table 2 (Tables 2-1 and 2-2).

TABLE 2-1 Magnetic layer forming composition Back PolyethyleneimineStearic acid Magnetic Non-magnetic coating Ferromagnetic Present orPresent or Tape layer layer layer powder absent of absent of Abrasiveamount (parts) thickness thickness thickness thickness Kind addingaddins A B C μm μm μm μm Example A1 BaFe Added Added 1.0 1.0 0.0 5.2 0.10.5 0.5 Example A2 BaFe Added Added 1.0 1.0 0.0 5.0 0.1 0.5 0.3 ExampleA3 BaFe Added Added 1.0 1.0 0.0 4.5 0.1 0.5 0.3 Example A4 BaFe AddedAdded 1.0 1.0 0.0 4.2 0.1 0.2 0.3 Example A5 BaFe Added Added 1.0 1.00.0 4.0 0.1 0.2 0.2 Example A6 BaFe Added Added 4.0 3.0 1.0 5.2 0.1 0.50.5 Example A7 BaFe Added Added 3.0 3.0 1.0 5.2 0.1 0.5 0.5 Example A8BaFe Added Added 6.0 4.0 1.0 5.2 0.1 0.5 0.5 Example A9 BaFe Added Added6.0 2.0 1.0 5.2 0.1 0.5 0.5 Example A10 BaFe Added Added 6.0 3.0 2.0 5.20.1 0.5 0.5 Example A11 BaFe Added Added 3.0 5.0 3.5 5.2 0.1 0.5 0.5Example A12 BaFe Added Added 9.5 1.0 0.5 5.2 0.1 0.5 0.5 Example A13BaFe Added Added 3.0 1.5 1.5 5.2 0.1 0.5 0.5 Example A14 BaFe AddedAdded 4.0 2.0 2.5 5.2 0.1 0.5 0.5 Example A15 BaFe Added Added 4.0 3.52.5 5.2 0.1 0.5 0.5 Example A16 SrFe1 Added Added 6.0 3.0 1.0 5.2 0.10.5 0.5 Example A17 SrFe2 Added Added 6.0 3.0 1.0 5.2 0.1 0.5 0.5Example A18 ε-iron Added Added 6.0 3.0 1.0 5.2 0.1 0.5 0.5 oxide ExampleA19 BaFe Added Added 3.0 3.0 1.0 4.0 0.1 0.2 0.2 Example A20 BaFe AddedAdded 3.0 3.0 1.0 4.0 0.1 0.2 0.2 Example A21 BaFe Added Added 3.0 3.01.0 4.0 0.1 0.2 0.2 Example A22 BaFe Added Added 3.0 3.0 1.0 4.0 0.1 0.20.2 Heat treatment conditions Standard Tension deviation of Non-magneticBending in case of AlFeSil the AlFeSil Standard SNR support elasticwinding abrasion abrasion deviation of reduction thickness modulusaround value_(45°) value curvature amount Recording μm Temperature Timefor core the core (μm) (μm) (mm/m) (dB) capacity Example A1 4.1 NoneNone None None 20 30 6 0.6 107 Example A2 4.1 None None None None 20 306 0.6 111 Example A3 3.6 None None None None 20 30 6 0.6 120 Example A43.6 None None None None 20 30 6 0.6 125 Example A5 3.5 None None NoneNone 20 30 6 0.6 129 Example A6 4.1 None None None None 25 30 6 0.8 107Example A7 4.1 None None None None 30 25 6 0.9 107 Example A8 4.1 NoneNone None None 37 18 6 0.8 107 Example A9 4.1 None None None None 32 206 0.6 107 Example A10 4.1 None None None None 40 18 6 0.8 107 ExampleA11 4.1 None None None None 50 30 6 0.9 107 Example A12 4.1 None NoneNone None 30 20 6 0.7 107 Example A13 4.1 None None None None 35 22 60.8 107 Example A14 4.1 None None None None 50 25 6 0.4 107 Example A154.1 None None None None 50 25 6 0.5 107 Example A16 4.1 None None NoneNone 28 18 6 0.6 107 Example A17 4.1 None None None None 28 18 6 0.6 107Example A18 4.1 None None None None 30 15 6 0.6 107 Example A19 3.5 50°C. 5 hours 0.8 GPa 0.6N 30 25 5 0.6 129 Example A20 3.5 60° C. 5 hours0.8 GPa 0.6N 30 25 4 0.4 129 Example A21 3.5 70° C. 5 hours 0.8 GPa 0.6N30 25 3 0.4 129 Example A22 3.5 70° C. 15 hours  0.8 GPa 0.8N 30 25 20.3 129

TABLE 2-2 Magnetic layer forming composition Back PolyethyleneimineStearic acid Magnetic Non-magnetic coating Ferromagnetic Present orPresent or Tape layer layer layer powder absent of absent of Abrasiveamount (parts) thickness thickness thickness thickness Kind addingaddins A B C μm μm μm μm Example B1 BaFe None Added 0.0 0.0 3.0 6.1 0.10.9 0.5 Example B2 BaFe None Added 0.0 0.0 5.0 6.1 0.1 0.9 0.5 ExampleB3 BaFe None Added 0.0 0.0 10.0 6.1 0.1 0.9 0.5 Example B4 BaFe NoneAdded 0.0 0.0 15.0 6.1 0.1 0.9 0.5 Example B5 BaFe None Added 7.0 4.03.0 6.1 0.1 0.9 0.5 Example B6 BaFe None Added 6.0 3.0 1.0 6.1 0.1 0.90.5 Example B7 BaFe Added Added 7.0 4.0 3.0 6.1 0.1 0.9 0.5 Example B8BaFe Added Added 1.0 0.5 0.0 6.1 0.1 0.9 0.5 Example B9 BaFe Added Added0.5 0.5 0.0 6.1 0.1 0.9 0.5 Example B10 BaFe Added Added 0.0 0.5 0.0 6.10.1 0.9 0.5 Example B11 BaFe Added Added 1.0 1.0 0.0 5.6 0.1 0.8 0.4Example B12 BaFe Added Added 4.0 3.0 1.0 5.6 0.1 0.8 0.4 Example B13BaFe Added Added 3.0 3.0 1.0 5.6 0.1 0.8 0.4 Example B14 BaFe AddedAdded 6.0 4.0 1.0 5.6 0.1 0.8 0.4 Example B15 BaFe Added Added 6.0 2.01.0 5.6 0.1 0.8 0.4 Example B16 BaFe Added Added 6.0 3.0 2.0 5.6 0.1 0.80.4 Example B17 BaFe Added Added 3.0 5.0 3.5 5.6 0.1 0.8 0.4 Example B18BaFe Added Added 9.5 1.0 0.5 5.6 0.1 0.8 0.4 Example B19 BaFe AddedAdded 3.0 1.5 1.5 5.6 0.1 0.8 0.4 Example B20 BaFe Added Added 4.0 2.02.5 5.6 0.1 0.8 0.4 Example B21 BaFe Added Added 4.0 3.5 2.5 5.6 0.1 0.80.4 Example B22 SrFe1 Added Added 6.0 3.0 1.0 5.6 0.1 0.8 0.4 ExampleB23 SrFe2 Added Added 6.0 3.0 1.0 5.6 0.1 0.8 0.4 Example B24 ε-ironAdded Added 6.0 3.0 1.0 5.6 0.1 0.8 0.4 oxide Example B25 BaFe AddedAdded 3.0 3.0 1.0 5.6 0.1 0.8 0.4 Example B26 BaFe Added Added 3.0 3.01.0 5.6 0.1 0.8 0.4 Example B27 BaFe Added Added 3.0 3.0 1.0 5.6 0.1 0.80.4 Example B28 BaFe Added Added 3.0 3.0 1.0 5.6 0.1 0.8 0.4 Heattreatment conditions Standard Tension deviation of Non-magnetic Bendingin case of AlFeSil the AlFeSil Standard SNR support elastic windingabrasion abrasion deviation of reduction thickness modulus aroundvalue_(45°) value curvature amount Recording μm Temperature Time forcore the core (μm) (μm) (mm/m) (dB) capacity Example B1 4.6 None NoneNone None 52 32 6 1.5 91 Example B2 4.6 None None None None 60 35 6 1.891 Example B3 4.6 None None None None 73 35 6 1.9 91 Example B4 4.6 NoneNone None None 79 36 6 2.0 91 Example B5 4.6 None None None None 70 32 61.6 91 Example B6 4.6 None None None None 53 32 6 1.6 91 Example B7 4.6None None None None 52 35 6 1.5 91 Example B8 4.6 None None None None 1910 6 2.2 91 Example B9 4.6 None None None None 10 5 6 2.5 91 Example B104.6 None None None None 5 5 6 3.0 91 Example B11 4.3 None None None None20 30 6 0.6 100 Example B12 4.3 None None None None 25 30 6 0.8 100Example B13 4.3 None None None None 30 25 6 0.9 100 Example B14 4.3 NoneNone None None 37 18 6 0.8 100 Example B15 4.3 None None None None 32 206 0.6 100 Example B16 4.3 None None None None 40 18 6 0.8 100 ExampleB17 4.3 None None None None 50 30 6 0.9 100 Example B18 4.3 None NoneNone None 30 20 6 0.7 100 Example B19 4.3 None None None None 35 22 60.8 100 Example B20 4.3 None None None None 50 25 6 0.4 100 Example B214.3 None None None None 50 25 6 0.5 100 Example B22 4.3 None None NoneNone 28 18 6 0.6 100 Example B23 4.3 None None None None 28 18 6 0.6 100Example B24 4.3 None None None None 30 15 6 0.6 100 Example B25 4.3 50°C. 5 hours 0.8 GPa 0.6N 30 25 5 0.6 100 Example B26 4.3 60° C. 5 hours0.8 GPa 0.6N 30 25 4 0.4 100 Example B27 4.3 70° C. 5 hours 0.8 GPa 0.6N30 25 3 0.4 100 Example B28 4.3 70° C. 15 hours  0.8 GPa 0.8N 30 25 20.3 100

From the results shown in Table 2, it can be confirmed that, in themagnetic tapes of Example A1 to Example A22, the deterioration inelectromagnetic conversion characteristics in a case where the magnetictape is caused to run at different head tilt angles was suppressed andthe magnetic tapes of Example A1 to Example A22 were preferable from aviewpoint of increasing the recording capacity.

A magnetic tape cartridge P-1 was manufactured by the same method as inExample A1 except that the homeotropic alignment process was notperformed in a case of manufacturing the magnetic tape.

A magnetic tape cartridge P-2 was manufactured by the same method as inExample A1 except that the magnetic field strength applied in thehomeotropic alignment process was changed to 0.5 T.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge P-1. For this sample piece, a verticalsquareness ratio was measured by the method described above using aTM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. asan oscillation sample type magnetic-flux meter. The vertical squarenessratio thus measured was 0.55.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge P-2. For this sample piece, a verticalsquareness ratio was measured in the same manner as described above. Thevertical squareness ratio thus measured was 0.65.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge of Example A1. For this sample piece, a verticalsquareness ratio was measured in the same manner as described above. Thevertical squareness ratio thus measured was 0.60.

Each of the magnetic tapes taken out from the above three magnetic tapecartridges was attached to each of the ½-inch reel testers, and theelectromagnetic conversion characteristics (signal-to-noise ratio (SNR))were evaluated by the following methods. As a result, regarding themagnetic tape taken out from the magnetic tape cartridge of Example A1,a value of SNR 2 dB higher than that of the magnetic tape (manufacturedwithout the homeotropic alignment process) taken out from the magnetictape cartridge P-1 was obtained. Regarding the magnetic tape taken outfrom the magnetic tape cartridge P-2, a value of SNR 4 dB higher thanthat of the magnetic tape taken out from the magnetic tape cartridge P-1was obtained.

In an environment of a temperature of 23° C. and a relative humidity of50%, a tension of 0.7 N was applied in the longitudinal direction of themagnetic tape, and recording and reproduction were performed for 10passes. A relative speed of the magnetic head and the magnetic tape wasset as 6 m/sec. The recording was performed by using a metal-in-gap(MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as therecording head and by setting a recording current as an optimalrecording current of each magnetic tape. The reproduction was performedusing a giant-magnetoresistive (GMR) head (element thickness of 15 nm,shield interval of 0.1 μm, reproducing element width of 0.8 μm) as thereproduction head. The head tilt angle was set to 0°. A signal having alinear recording density of 300 kfci was recorded, and the reproductionsignal was measured with a spectrum analyzer manufactured by ShibaSokuCo., Ltd. As the signal, a sufficiently stabilized portion of the signalafter starting the running of the magnetic tape was used.

One aspect of the invention is advantageous in a technical field ofvarious data storages.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer containing a ferromagnetic powder, whereina tape thickness of the magnetic tape is 5.2 μm or less, and in anenvironment with a temperature of 23° C. and a relative humidity of 50%,an AlFeSil abrasion value_(45°) of a surface of the magnetic layermeasured at a tilt angle of 45° of an AlFeSil prism is 20 μm to 50 μm, astandard deviation of an AlFeSil abrasion value of the surface of themagnetic layer measured at each of tilt angles of 0°, 15°, 30°, and 45°of the AlFeSil prism is 30 μm or less, and the tilt angle of the AlFeSilprism is an angle formed by a longitudinal direction of the AlFeSilprism and a width direction of the magnetic tape.
 2. The magnetic tapeaccording to claim 1, wherein the standard deviation of the AlFeSilabrasion value is 15 μm to 30 μm.
 3. The magnetic tape according toclaim 1, wherein the tape thickness is 4.0 μm to 5.2 μm.
 4. The magnetictape according to claim 1, wherein the tape thickness is 4.0 μm to 5.0μm.
 5. The magnetic tape according to claim 1, wherein a standarddeviation of curvature of the magnetic tape in a longitudinal directionis 5 mm/m or less.
 6. The magnetic tape according to claim 1, whereinthe magnetic layer contains one or more kinds of non-magnetic powder. 7.The magnetic tape according to claim 6, wherein the non-magnetic powderincludes an alumina powder.
 8. The magnetic tape according to claim 1,further comprising: a non-magnetic layer containing a non-magneticpowder between the non-magnetic support and the magnetic layer.
 9. Themagnetic tape according to claim 8, wherein a thickness of thenon-magnetic layer is 0.1 μm to 0.7 μm.
 10. The magnetic tape accordingto claim 1, further comprising: a back coating layer containing anon-magnetic powder on a surface side of the non-magnetic supportopposite to a surface side provided with the magnetic layer.
 11. Themagnetic tape device according to claim 1, wherein a vertical squarenessratio of the magnetic tape is 0.60 or more.
 12. The magnetic tape deviceaccording to claim 1, wherein a vertical squareness ratio of themagnetic tape is 0.65 or more.
 13. A magnetic tape cartridge comprising:the magnetic tape according to claim
 1. 14. A magnetic tape devicecomprising: the magnetic tape according to claim
 1. 15. The magnetictape device according to claim 14, further comprising: a magnetic head,wherein the magnetic head includes a module including an element arrayhaving a plurality of magnetic head elements between a pair of servosignal reading elements, and the magnetic tape device changes an angle θformed by an axis of the element array with respect to the widthdirection of the magnetic tape during running of the magnetic tape inthe magnetic tape device.